diff --git a/asynq_test.go b/asynq_test.go
index 3f6675c..3aff019 100644
--- a/asynq_test.go
+++ b/asynq_test.go
@@ -5,7 +5,6 @@
 package asynq
 
 import (
-	"os"
 	"sort"
 	"testing"
 
@@ -24,7 +23,7 @@ const (
 	redisDB   = 14
 )
 
-var testLogger = log.NewLogger(os.Stderr)
+var testLogger = log.NewLogger(nil)
 
 func setup(tb testing.TB) *redis.Client {
 	tb.Helper()
diff --git a/heartbeat.go b/heartbeat.go
index b89845c..61f7908 100644
--- a/heartbeat.go
+++ b/heartbeat.go
@@ -9,12 +9,13 @@ import (
 	"time"
 
 	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
 )
 
 // heartbeater is responsible for writing process info to redis periodically to
 // indicate that the background worker process is up.
 type heartbeater struct {
-	logger Logger
+	logger *log.Logger
 	broker base.Broker
 
 	ss *base.ServerState
@@ -26,7 +27,7 @@ type heartbeater struct {
 	interval time.Duration
 }
 
-func newHeartbeater(l Logger, b base.Broker, ss *base.ServerState, interval time.Duration) *heartbeater {
+func newHeartbeater(l *log.Logger, b base.Broker, ss *base.ServerState, interval time.Duration) *heartbeater {
 	return &heartbeater{
 		logger:   l,
 		broker:   b,
@@ -67,6 +68,6 @@ func (h *heartbeater) beat() {
 	// and short enough to expire quickly once the process is shut down or killed.
 	err := h.broker.WriteServerState(h.ss, h.interval*2)
 	if err != nil {
-		h.logger.Error("could not write heartbeat data: %v", err)
+		h.logger.Errorf("could not write heartbeat data: %v", err)
 	}
 }
diff --git a/internal/log/log.go b/internal/log/log.go
index ba3b368..7fdd5bf 100644
--- a/internal/log/log.go
+++ b/internal/log/log.go
@@ -6,52 +6,106 @@
 package log
 
 import (
+	"fmt"
 	"io"
 	stdlog "log"
 	"os"
 )
 
-// NewLogger creates and returns a new instance of Logger.
-func NewLogger(out io.Writer) *Logger {
-	return &Logger{
-		stdlog.New(out, "", stdlog.Ldate|stdlog.Ltime|stdlog.Lmicroseconds|stdlog.LUTC),
-	}
+// Base supports logging with various log levels.
+type Base interface {
+	// Debug logs a message at Debug level.
+	Debug(args ...interface{})
+
+	// Info logs a message at Info level.
+	Info(args ...interface{})
+
+	// Warn logs a message at Warning level.
+	Warn(args ...interface{})
+
+	// Error logs a message at Error level.
+	Error(args ...interface{})
+
+	// Fatal logs a message at Fatal level
+	// and process will exit with status set to 1.
+	Fatal(args ...interface{})
 }
 
-// Logger is a wrapper object around log.Logger from the standard library.
+// baseLogger is a wrapper object around log.Logger from the standard library.
 // It supports logging at various log levels.
-type Logger struct {
+type baseLogger struct {
 	*stdlog.Logger
 }
 
 // Debug logs a message at Debug level.
-func (l *Logger) Debug(format string, args ...interface{}) {
-	format = "DEBUG: " + format
-	l.Printf(format, args...)
+func (l *baseLogger) Debug(args ...interface{}) {
+	l.prefixPrint("DEBUG: ", args...)
 }
 
 // Info logs a message at Info level.
-func (l *Logger) Info(format string, args ...interface{}) {
-	format = "INFO: " + format
-	l.Printf(format, args...)
+func (l *baseLogger) Info(args ...interface{}) {
+	l.prefixPrint("INFO: ", args...)
 }
 
 // Warn logs a message at Warning level.
-func (l *Logger) Warn(format string, args ...interface{}) {
-	format = "WARN: " + format
-	l.Printf(format, args...)
+func (l *baseLogger) Warn(args ...interface{}) {
+	l.prefixPrint("WARN: ", args...)
 }
 
 // Error logs a message at Error level.
-func (l *Logger) Error(format string, args ...interface{}) {
-	format = "ERROR: " + format
-	l.Printf(format, args...)
+func (l *baseLogger) Error(args ...interface{}) {
+	l.prefixPrint("ERROR: ", args...)
 }
 
 // Fatal logs a message at Fatal level
 // and process will exit with status set to 1.
-func (l *Logger) Fatal(format string, args ...interface{}) {
-	format = "FATAL: " + format
-	l.Printf(format, args...)
+func (l *baseLogger) Fatal(args ...interface{}) {
+	l.prefixPrint("FATAL: ", args...)
 	os.Exit(1)
 }
+
+func (l *baseLogger) prefixPrint(prefix string, args ...interface{}) {
+	args = append([]interface{}{prefix}, args...)
+	l.Print(args...)
+}
+
+// newBase creates and returns a new instance of baseLogger.
+func newBase(out io.Writer) *baseLogger {
+	prefix := fmt.Sprintf("asynq: pid=%d ", os.Getpid())
+	return &baseLogger{
+		stdlog.New(out, prefix, stdlog.Ldate|stdlog.Ltime|stdlog.Lmicroseconds|stdlog.LUTC),
+	}
+}
+
+// NewLogger creates and returns a new instance of Logger.
+func NewLogger(base Base) *Logger {
+	if base == nil {
+		base = newBase(os.Stderr)
+	}
+	return &Logger{base}
+}
+
+// Logger logs message to io.Writer with various log levels.
+type Logger struct {
+	Base
+}
+
+func (l *Logger) Debugf(format string, args ...interface{}) {
+	l.Debug(fmt.Sprintf(format, args...))
+}
+
+func (l *Logger) Infof(format string, args ...interface{}) {
+	l.Info(fmt.Sprintf(format, args...))
+}
+
+func (l *Logger) Warnf(format string, args ...interface{}) {
+	l.Warn(fmt.Sprintf(format, args...))
+}
+
+func (l *Logger) Errorf(format string, args ...interface{}) {
+	l.Error(fmt.Sprintf(format, args...))
+}
+
+func (l *Logger) Fatalf(format string, args ...interface{}) {
+	l.Fatal(fmt.Sprintf(format, args...))
+}
diff --git a/internal/log/log_test.go b/internal/log/log_test.go
index 3c96418..2285ae3 100644
--- a/internal/log/log_test.go
+++ b/internal/log/log_test.go
@@ -13,6 +13,7 @@ import (
 
 // regexp for timestamps
 const (
+	rgxPID          = `[0-9]+`
 	rgxdate         = `[0-9][0-9][0-9][0-9]/[0-9][0-9]/[0-9][0-9]`
 	rgxtime         = `[0-9][0-9]:[0-9][0-9]:[0-9][0-9]`
 	rgxmicroseconds = `\.[0-9][0-9][0-9][0-9][0-9][0-9]`
@@ -27,20 +28,22 @@ type tester struct {
 func TestLoggerDebug(t *testing.T) {
 	tests := []tester{
 		{
-			desc:        "without trailing newline, logger adds newline",
-			message:     "hello, world!",
-			wantPattern: fmt.Sprintf("^%s %s%s DEBUG: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "without trailing newline, logger adds newline",
+			message: "hello, world!",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s DEBUG: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 		{
-			desc:        "with trailing newline, logger preserves newline",
-			message:     "hello, world!\n",
-			wantPattern: fmt.Sprintf("^%s %s%s DEBUG: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "with trailing newline, logger preserves newline",
+			message: "hello, world!\n",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s DEBUG: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 	}
 
 	for _, tc := range tests {
 		var buf bytes.Buffer
-		logger := NewLogger(&buf)
+		logger := NewLogger(newBase(&buf))
 
 		logger.Debug(tc.message)
 
@@ -50,7 +53,7 @@ func TestLoggerDebug(t *testing.T) {
 			t.Fatal("pattern did not compile:", err)
 		}
 		if !matched {
-			t.Errorf("logger.info(%q) outputted %q, should match pattern %q",
+			t.Errorf("logger.Debug(%q) outputted %q, should match pattern %q",
 				tc.message, got, tc.wantPattern)
 		}
 	}
@@ -59,20 +62,22 @@ func TestLoggerDebug(t *testing.T) {
 func TestLoggerInfo(t *testing.T) {
 	tests := []tester{
 		{
-			desc:        "without trailing newline, logger adds newline",
-			message:     "hello, world!",
-			wantPattern: fmt.Sprintf("^%s %s%s INFO: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "without trailing newline, logger adds newline",
+			message: "hello, world!",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s INFO: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 		{
-			desc:        "with trailing newline, logger preserves newline",
-			message:     "hello, world!\n",
-			wantPattern: fmt.Sprintf("^%s %s%s INFO: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "with trailing newline, logger preserves newline",
+			message: "hello, world!\n",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s INFO: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 	}
 
 	for _, tc := range tests {
 		var buf bytes.Buffer
-		logger := NewLogger(&buf)
+		logger := NewLogger(newBase(&buf))
 
 		logger.Info(tc.message)
 
@@ -82,7 +87,7 @@ func TestLoggerInfo(t *testing.T) {
 			t.Fatal("pattern did not compile:", err)
 		}
 		if !matched {
-			t.Errorf("logger.info(%q) outputted %q, should match pattern %q",
+			t.Errorf("logger.Info(%q) outputted %q, should match pattern %q",
 				tc.message, got, tc.wantPattern)
 		}
 	}
@@ -91,20 +96,22 @@ func TestLoggerInfo(t *testing.T) {
 func TestLoggerWarn(t *testing.T) {
 	tests := []tester{
 		{
-			desc:        "without trailing newline, logger adds newline",
-			message:     "hello, world!",
-			wantPattern: fmt.Sprintf("^%s %s%s WARN: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "without trailing newline, logger adds newline",
+			message: "hello, world!",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s WARN: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 		{
-			desc:        "with trailing newline, logger preserves newline",
-			message:     "hello, world!\n",
-			wantPattern: fmt.Sprintf("^%s %s%s WARN: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "with trailing newline, logger preserves newline",
+			message: "hello, world!\n",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s WARN: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 	}
 
 	for _, tc := range tests {
 		var buf bytes.Buffer
-		logger := NewLogger(&buf)
+		logger := NewLogger(newBase(&buf))
 
 		logger.Warn(tc.message)
 
@@ -114,7 +121,7 @@ func TestLoggerWarn(t *testing.T) {
 			t.Fatal("pattern did not compile:", err)
 		}
 		if !matched {
-			t.Errorf("logger.info(%q) outputted %q, should match pattern %q",
+			t.Errorf("logger.Warn(%q) outputted %q, should match pattern %q",
 				tc.message, got, tc.wantPattern)
 		}
 	}
@@ -123,20 +130,22 @@ func TestLoggerWarn(t *testing.T) {
 func TestLoggerError(t *testing.T) {
 	tests := []tester{
 		{
-			desc:        "without trailing newline, logger adds newline",
-			message:     "hello, world!",
-			wantPattern: fmt.Sprintf("^%s %s%s ERROR: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "without trailing newline, logger adds newline",
+			message: "hello, world!",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s ERROR: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 		{
-			desc:        "with trailing newline, logger preserves newline",
-			message:     "hello, world!\n",
-			wantPattern: fmt.Sprintf("^%s %s%s ERROR: hello, world!\n$", rgxdate, rgxtime, rgxmicroseconds),
+			desc:    "with trailing newline, logger preserves newline",
+			message: "hello, world!\n",
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s ERROR: hello, world!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
 		},
 	}
 
 	for _, tc := range tests {
 		var buf bytes.Buffer
-		logger := NewLogger(&buf)
+		logger := NewLogger(newBase(&buf))
 
 		logger.Error(tc.message)
 
@@ -146,8 +155,131 @@ func TestLoggerError(t *testing.T) {
 			t.Fatal("pattern did not compile:", err)
 		}
 		if !matched {
-			t.Errorf("logger.info(%q) outputted %q, should match pattern %q",
+			t.Errorf("logger.Error(%q) outputted %q, should match pattern %q",
 				tc.message, got, tc.wantPattern)
 		}
 	}
 }
+
+type formatTester struct {
+	desc        string
+	format      string
+	args        []interface{}
+	wantPattern string // regexp that log output must match
+}
+
+func TestLoggerDebugf(t *testing.T) {
+	tests := []formatTester{
+		{
+			desc:   "Formats message with DEBUG prefix",
+			format: "hello, %s!",
+			args:   []interface{}{"Gopher"},
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s DEBUG: hello, Gopher!\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
+		},
+	}
+
+	for _, tc := range tests {
+		var buf bytes.Buffer
+		logger := NewLogger(newBase(&buf))
+
+		logger.Debugf(tc.format, tc.args...)
+
+		got := buf.String()
+		matched, err := regexp.MatchString(tc.wantPattern, got)
+		if err != nil {
+			t.Fatal("pattern did not compile:", err)
+		}
+		if !matched {
+			t.Errorf("logger.Debugf(%q, %v) outputted %q, should match pattern %q",
+				tc.format, tc.args, got, tc.wantPattern)
+		}
+	}
+}
+
+func TestLoggerInfof(t *testing.T) {
+	tests := []formatTester{
+		{
+			desc:   "Formats message with INFO prefix",
+			format: "%d,%d,%d",
+			args:   []interface{}{1, 2, 3},
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s INFO: 1,2,3\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
+		},
+	}
+
+	for _, tc := range tests {
+		var buf bytes.Buffer
+		logger := NewLogger(newBase(&buf))
+
+		logger.Infof(tc.format, tc.args...)
+
+		got := buf.String()
+		matched, err := regexp.MatchString(tc.wantPattern, got)
+		if err != nil {
+			t.Fatal("pattern did not compile:", err)
+		}
+		if !matched {
+			t.Errorf("logger.Infof(%q, %v) outputted %q, should match pattern %q",
+				tc.format, tc.args, got, tc.wantPattern)
+		}
+	}
+}
+
+func TestLoggerWarnf(t *testing.T) {
+	tests := []formatTester{
+		{
+			desc:   "Formats message with WARN prefix",
+			format: "hello, %s",
+			args:   []interface{}{"Gophers"},
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s WARN: hello, Gophers\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
+		},
+	}
+
+	for _, tc := range tests {
+		var buf bytes.Buffer
+		logger := NewLogger(newBase(&buf))
+
+		logger.Warnf(tc.format, tc.args...)
+
+		got := buf.String()
+		matched, err := regexp.MatchString(tc.wantPattern, got)
+		if err != nil {
+			t.Fatal("pattern did not compile:", err)
+		}
+		if !matched {
+			t.Errorf("logger.Warnf(%q, %v) outputted %q, should match pattern %q",
+				tc.format, tc.args, got, tc.wantPattern)
+		}
+	}
+}
+
+func TestLoggerErrorf(t *testing.T) {
+	tests := []formatTester{
+		{
+			desc:   "Formats message with ERROR prefix",
+			format: "hello, %s",
+			args:   []interface{}{"Gophers"},
+			wantPattern: fmt.Sprintf("^asynq: pid=%s %s %s%s ERROR: hello, Gophers\n$",
+				rgxPID, rgxdate, rgxtime, rgxmicroseconds),
+		},
+	}
+
+	for _, tc := range tests {
+		var buf bytes.Buffer
+		logger := NewLogger(newBase(&buf))
+
+		logger.Errorf(tc.format, tc.args...)
+
+		got := buf.String()
+		matched, err := regexp.MatchString(tc.wantPattern, got)
+		if err != nil {
+			t.Fatal("pattern did not compile:", err)
+		}
+		if !matched {
+			t.Errorf("logger.Errorf(%q, %v) outputted %q, should match pattern %q",
+				tc.format, tc.args, got, tc.wantPattern)
+		}
+	}
+}
diff --git a/processor.go b/processor.go
index f0bd799..092fd37 100644
--- a/processor.go
+++ b/processor.go
@@ -13,12 +13,13 @@ import (
 	"time"
 
 	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
 	"github.com/hibiken/asynq/internal/rdb"
 	"golang.org/x/time/rate"
 )
 
 type processor struct {
-	logger Logger
+	logger *log.Logger
 	broker base.Broker
 
 	ss *base.ServerState
@@ -64,7 +65,7 @@ type processor struct {
 type retryDelayFunc func(n int, err error, task *Task) time.Duration
 
 type newProcessorParams struct {
-	logger          Logger
+	logger          *log.Logger
 	broker          base.Broker
 	ss              *base.ServerState
 	retryDelayFunc  retryDelayFunc
@@ -170,7 +171,7 @@ func (p *processor) exec() {
 	}
 	if err != nil {
 		if p.errLogLimiter.Allow() {
-			p.logger.Error("Dequeue error: %v", err)
+			p.logger.Errorf("Dequeue error: %v", err)
 		}
 		return
 	}
@@ -202,7 +203,7 @@ func (p *processor) exec() {
 			select {
 			case <-p.quit:
 				// time is up, quit this worker goroutine.
-				p.logger.Warn("Quitting worker. task id=%s", msg.ID)
+				p.logger.Warnf("Quitting worker. task id=%s", msg.ID)
 				return
 			case resErr := <-resCh:
 				// Note: One of three things should happen.
@@ -231,17 +232,17 @@ func (p *processor) exec() {
 func (p *processor) restore() {
 	n, err := p.broker.RequeueAll()
 	if err != nil {
-		p.logger.Error("Could not restore unfinished tasks: %v", err)
+		p.logger.Errorf("Could not restore unfinished tasks: %v", err)
 	}
 	if n > 0 {
-		p.logger.Info("Restored %d unfinished tasks back to queue", n)
+		p.logger.Infof("Restored %d unfinished tasks back to queue", n)
 	}
 }
 
 func (p *processor) requeue(msg *base.TaskMessage) {
 	err := p.broker.Requeue(msg)
 	if err != nil {
-		p.logger.Error("Could not push task id=%s back to queue: %v", msg.ID, err)
+		p.logger.Errorf("Could not push task id=%s back to queue: %v", msg.ID, err)
 	}
 }
 
@@ -249,7 +250,7 @@ func (p *processor) markAsDone(msg *base.TaskMessage) {
 	err := p.broker.Done(msg)
 	if err != nil {
 		errMsg := fmt.Sprintf("Could not remove task id=%s from %q", msg.ID, base.InProgressQueue)
-		p.logger.Warn("%s; Will retry syncing", errMsg)
+		p.logger.Warnf("%s; Will retry syncing", errMsg)
 		p.syncRequestCh <- &syncRequest{
 			fn: func() error {
 				return p.broker.Done(msg)
@@ -265,7 +266,7 @@ func (p *processor) retry(msg *base.TaskMessage, e error) {
 	err := p.broker.Retry(msg, retryAt, e.Error())
 	if err != nil {
 		errMsg := fmt.Sprintf("Could not move task id=%s from %q to %q", msg.ID, base.InProgressQueue, base.RetryQueue)
-		p.logger.Warn("%s; Will retry syncing", errMsg)
+		p.logger.Warnf("%s; Will retry syncing", errMsg)
 		p.syncRequestCh <- &syncRequest{
 			fn: func() error {
 				return p.broker.Retry(msg, retryAt, e.Error())
@@ -276,11 +277,11 @@ func (p *processor) retry(msg *base.TaskMessage, e error) {
 }
 
 func (p *processor) kill(msg *base.TaskMessage, e error) {
-	p.logger.Warn("Retry exhausted for task id=%s", msg.ID)
+	p.logger.Warnf("Retry exhausted for task id=%s", msg.ID)
 	err := p.broker.Kill(msg, e.Error())
 	if err != nil {
 		errMsg := fmt.Sprintf("Could not move task id=%s from %q to %q", msg.ID, base.InProgressQueue, base.DeadQueue)
-		p.logger.Warn("%s; Will retry syncing", errMsg)
+		p.logger.Warnf("%s; Will retry syncing", errMsg)
 		p.syncRequestCh <- &syncRequest{
 			fn: func() error {
 				return p.broker.Kill(msg, e.Error())
diff --git a/scheduler.go b/scheduler.go
index 8f4f860..aa0a36d 100644
--- a/scheduler.go
+++ b/scheduler.go
@@ -9,10 +9,11 @@ import (
 	"time"
 
 	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
 )
 
 type scheduler struct {
-	logger Logger
+	logger *log.Logger
 	broker base.Broker
 
 	// channel to communicate back to the long running "scheduler" goroutine.
@@ -25,7 +26,7 @@ type scheduler struct {
 	qnames []string
 }
 
-func newScheduler(l Logger, b base.Broker, avgInterval time.Duration, qcfg map[string]int) *scheduler {
+func newScheduler(l *log.Logger, b base.Broker, avgInterval time.Duration, qcfg map[string]int) *scheduler {
 	var qnames []string
 	for q := range qcfg {
 		qnames = append(qnames, q)
@@ -64,6 +65,6 @@ func (s *scheduler) start(wg *sync.WaitGroup) {
 
 func (s *scheduler) exec() {
 	if err := s.broker.CheckAndEnqueue(s.qnames...); err != nil {
-		s.logger.Error("Could not enqueue scheduled tasks: %v", err)
+		s.logger.Errorf("Could not enqueue scheduled tasks: %v", err)
 	}
 }
diff --git a/server.go b/server.go
index 50fc27a..86ff04f 100644
--- a/server.go
+++ b/server.go
@@ -35,7 +35,7 @@ import (
 type Server struct {
 	ss *base.ServerState
 
-	logger Logger
+	logger *log.Logger
 
 	broker base.Broker
 
@@ -133,23 +133,23 @@ func (fn ErrorHandlerFunc) HandleError(task *Task, err error, retried, maxRetry
 	fn(task, err, retried, maxRetry)
 }
 
-// Logger implements logging with various log levels.
+// Logger supports logging with various log levels.
 type Logger interface {
 	// Debug logs a message at Debug level.
-	Debug(format string, args ...interface{})
+	Debug(args ...interface{})
 
 	// Info logs a message at Info level.
-	Info(format string, args ...interface{})
+	Info(args ...interface{})
 
 	// Warn logs a message at Warning level.
-	Warn(format string, args ...interface{})
+	Warn(args ...interface{})
 
 	// Error logs a message at Error level.
-	Error(format string, args ...interface{})
+	Error(args ...interface{})
 
 	// Fatal logs a message at Fatal level
 	// and process will exit with status set to 1.
-	Fatal(format string, args ...interface{})
+	Fatal(args ...interface{})
 }
 
 // Formula taken from https://github.com/mperham/sidekiq.
@@ -185,10 +185,6 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 	if len(queues) == 0 {
 		queues = defaultQueueConfig
 	}
-	logger := cfg.Logger
-	if logger == nil {
-		logger = log.NewLogger(os.Stderr)
-	}
 	shutdownTimeout := cfg.ShutdownTimeout
 	if shutdownTimeout == 0 {
 		shutdownTimeout = defaultShutdownTimeout
@@ -201,6 +197,7 @@ func NewServer(r RedisConnOpt, cfg Config) *Server {
 	pid := os.Getpid()
 
 	rdb := rdb.NewRDB(createRedisClient(r))
+	logger := log.NewLogger(cfg.Logger)
 	ss := base.NewServerState(host, pid, n, queues, cfg.StrictPriority)
 	syncCh := make(chan *syncRequest)
 	cancels := base.NewCancelations()
@@ -291,13 +288,6 @@ func (srv *Server) Start(handler Handler) error {
 	srv.ss.SetStatus(base.StatusRunning)
 	srv.processor.handler = handler
 
-	type prefixLogger interface {
-		SetPrefix(prefix string)
-	}
-	// If logger supports setting prefix, then set prefix for log output.
-	if l, ok := srv.logger.(prefixLogger); ok {
-		l.SetPrefix(fmt.Sprintf("asynq: pid=%d ", os.Getpid()))
-	}
 	srv.logger.Info("Starting processing")
 
 	srv.heartbeater.start(&srv.wg)
diff --git a/subscriber.go b/subscriber.go
index c72ac89..be7a010 100644
--- a/subscriber.go
+++ b/subscriber.go
@@ -10,10 +10,11 @@ import (
 
 	"github.com/go-redis/redis/v7"
 	"github.com/hibiken/asynq/internal/base"
+	"github.com/hibiken/asynq/internal/log"
 )
 
 type subscriber struct {
-	logger Logger
+	logger *log.Logger
 	broker base.Broker
 
 	// channel to communicate back to the long running "subscriber" goroutine.
@@ -26,7 +27,7 @@ type subscriber struct {
 	retryTimeout time.Duration
 }
 
-func newSubscriber(l Logger, b base.Broker, cancelations *base.Cancelations) *subscriber {
+func newSubscriber(l *log.Logger, b base.Broker, cancelations *base.Cancelations) *subscriber {
 	return &subscriber{
 		logger:       l,
 		broker:       b,
@@ -54,7 +55,7 @@ func (s *subscriber) start(wg *sync.WaitGroup) {
 		for {
 			pubsub, err = s.broker.CancelationPubSub()
 			if err != nil {
-				s.logger.Error("cannot subscribe to cancelation channel: %v", err)
+				s.logger.Errorf("cannot subscribe to cancelation channel: %v", err)
 				select {
 				case <-time.After(s.retryTimeout):
 					continue
diff --git a/syncer.go b/syncer.go
index 1ddef9b..018196d 100644
--- a/syncer.go
+++ b/syncer.go
@@ -7,12 +7,14 @@ package asynq
 import (
 	"sync"
 	"time"
+
+	"github.com/hibiken/asynq/internal/log"
 )
 
 // syncer is responsible for queuing up failed requests to redis and retry
 // those requests to sync state between the background process and redis.
 type syncer struct {
-	logger Logger
+	logger *log.Logger
 
 	requestsCh <-chan *syncRequest
 
@@ -28,7 +30,7 @@ type syncRequest struct {
 	errMsg string       // error message
 }
 
-func newSyncer(l Logger, requestsCh <-chan *syncRequest, interval time.Duration) *syncer {
+func newSyncer(l *log.Logger, requestsCh <-chan *syncRequest, interval time.Duration) *syncer {
 	return &syncer{
 		logger:     l,
 		requestsCh: requestsCh,