diff --git a/logging/example_test.go b/logging/example_test.go
index a013ed1..eb3aa73 100644
--- a/logging/example_test.go
+++ b/logging/example_test.go
@@ -3,7 +3,7 @@ package logging_test
 import "github.com/kisom/goutils/logging"
 
 var log = logging.Init()
-var olog = logging.New("subsystem #42", logging.LevelNotice)
+var olog, _ = logging.New("subsystem #42", logging.LevelNotice)
 
 func Example() {
 	log.Notice("Hello, world.")
diff --git a/logging/levels.go b/logging/levels.go
index 209cac1..8efd583 100644
--- a/logging/levels.go
+++ b/logging/levels.go
@@ -64,7 +64,7 @@ var levelPrefix = [...]string{
 var DateFormat = "2006-01-02T15:03:04-0700"
 
 func (l *Logger) outputf(level Level, format string, v []interface{}) {
-	if !logConfig.registered[l.domain] {
+	if !l.Enabled() {
 		return
 	}
 
@@ -81,7 +81,7 @@ func (l *Logger) outputf(level Level, format string, v []interface{}) {
 }
 
 func (l *Logger) output(level Level, v []interface{}) {
-	if !logConfig.registered[l.domain] {
+	if !l.Enabled() {
 		return
 	}
 
diff --git a/logging/log.go b/logging/log.go
index da600a0..a7e7df9 100644
--- a/logging/log.go
+++ b/logging/log.go
@@ -9,16 +9,17 @@ import (
 	"io"
 	"os"
 	"path/filepath"
+	"strings"
 	"sync"
 
 	"github.com/kisom/goutils/mwc"
 )
 
 var logConfig = struct {
-	registered map[string]bool
+	registered map[string]*Logger
 	lock       *sync.Mutex
 }{
-	registered: map[string]bool{},
+	registered: map[string]*Logger{},
 	lock:       new(sync.Mutex),
 }
 
@@ -28,16 +29,19 @@ const DefaultLevel = LevelNotice
 // Init returns a new default logger. The domain is set to the
 // program's name, and the default logging level is used.
 func Init() *Logger {
-	return New(filepath.Base(os.Args[0]), DefaultLevel)
+	l, _ := New(filepath.Base(os.Args[0]), DefaultLevel)
+	return l
 }
 
 // A Logger writes logs on behalf of a particular domain at a certain
 // level.
 type Logger struct {
-	domain string
-	level  Level
-	out    io.WriteCloser
-	err    io.WriteCloser
+	enabled bool
+	lock    *sync.Mutex
+	domain  string
+	level   Level
+	out     io.WriteCloser
+	err     io.WriteCloser
 }
 
 // Close closes the log's writers and suppresses the logger.
@@ -55,15 +59,30 @@ func (l *Logger) Close() error {
 func Suppress(domain string) {
 	logConfig.lock.Lock()
 	defer logConfig.lock.Unlock()
-	logConfig.registered[domain] = false
+	l, ok := logConfig.registered[domain]
+	if ok {
+		l.Suppress()
+	}
+}
+
+// SuppressPrefix suppress logs whose domain is prefixed with the
+// prefix.
+func SuppressPrefix(prefix string) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	for domain, l := range logConfig.registered {
+		if strings.HasPrefix(domain, prefix) {
+			l.Suppress()
+		}
+	}
 }
 
 // SuppressAll suppresses all logging output.
 func SuppressAll() {
 	logConfig.lock.Lock()
 	defer logConfig.lock.Unlock()
-	for domain := range logConfig.registered {
-		logConfig.registered[domain] = false
+	for _, l := range logConfig.registered {
+		l.Suppress()
 	}
 }
 
@@ -71,48 +90,90 @@ func SuppressAll() {
 func Enable(domain string) {
 	logConfig.lock.Lock()
 	defer logConfig.lock.Unlock()
-	logConfig.registered[domain] = true
+	l, ok := logConfig.registered[domain]
+	if ok {
+		l.Enable()
+	}
+}
+
+// EnablePrefix enables logs whose domain is prefixed with prefix.
+func EnablePrefix(prefix string) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	for domain, l := range logConfig.registered {
+		if strings.HasPrefix(domain, prefix) {
+			l.Enable()
+		}
+	}
 }
 
 // EnableAll enables all domains.
 func EnableAll() {
 	logConfig.lock.Lock()
 	defer logConfig.lock.Unlock()
-	for domain := range logConfig.registered {
-		logConfig.registered[domain] = true
+	for _, l := range logConfig.registered {
+		l.Enable()
 	}
 }
 
 // New returns a new logger that writes to standard output for Notice
-// and below and standard error for levels above Notice.
-func New(domain string, level Level) *Logger {
-	l := &Logger{
+// and below and standard error for levels above Notice. If a logger
+// with the same domain exists, the logger will set its level to level
+// and return the logger; in this case, the registered return value
+// will be true.
+func New(domain string, level Level) (l *Logger, registered bool) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+
+	l = logConfig.registered[domain]
+	if l != nil {
+		l.SetLevel(level)
+		return l, true
+	}
+
+	l = &Logger{
 		domain: domain,
 		level:  level,
 		out:    os.Stdout,
 		err:    os.Stderr,
+		lock:   new(sync.Mutex),
 	}
 
-	Enable(domain)
-	return l
+	l.Enable()
+	logConfig.registered[domain] = l
+	return l, false
 }
 
-// NewWriters returns a new logger that writes to the w io.WriteCloser for
-// Notice and below and to the e io.WriteCloser for levels above Notice. If e is nil, w will be used.
-func NewFromWriters(domain string, level Level, w, e io.WriteCloser) *Logger {
+// NewWriters returns a new logger that writes to the w io.WriteCloser
+// for Notice and below and to the e io.WriteCloser for levels above
+// Notice. If e is nil, w will be used. If a logger with the same
+// domain exists, the logger will set its level to level and return
+// the logger; in this case, the registered return value will be true.
+func NewFromWriters(domain string, level Level, w, e io.WriteCloser) (l *Logger, registered bool) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+
+	l = logConfig.registered[domain]
+	if l != nil {
+		l.SetLevel(level)
+		return l, true
+	}
+
 	if e == nil {
 		e = w
 	}
 
-	l := &Logger{
+	l = &Logger{
 		domain: domain,
 		level:  level,
 		out:    w,
 		err:    e,
+		lock:   new(sync.Mutex),
 	}
 
-	Enable(domain)
-	return l
+	l.Enable()
+	logConfig.registered[domain] = l
+	return l, false
 }
 
 // NewFile returns a new logger that opens the files for writing. If
@@ -122,6 +183,7 @@ func NewFromFile(domain string, level Level, outFile, errFile string, multiplex
 	l := &Logger{
 		domain: domain,
 		level:  level,
+		lock:   new(sync.Mutex),
 	}
 
 	outf, err := os.OpenFile(outFile, os.O_APPEND|os.O_CREATE|os.O_WRONLY, 0644)
@@ -148,12 +210,21 @@ func NewFromFile(domain string, level Level, outFile, errFile string, multiplex
 
 // Enable allows output from the logger.
 func (l *Logger) Enable() {
-	Enable(l.domain)
+	l.lock.Lock()
+	defer l.lock.Unlock()
+	l.enabled = true
+}
+
+// Enabled returns true if the logger is enabled.
+func (l *Logger) Enabled() bool {
+	return l.enabled
 }
 
 // Suppress ignores output from the logger.
 func (l *Logger) Suppress() {
-	Suppress(l.domain)
+	l.lock.Lock()
+	defer l.lock.Unlock()
+	l.enabled = false
 }
 
 // Domain returns the domain of the logger.
@@ -163,5 +234,7 @@ func (l *Logger) Domain() string {
 
 // SetLevel changes the level of the logger.
 func (l *Logger) SetLevel(level Level) {
+	l.lock.Lock()
+	defer l.lock.Unlock()
 	l.level = level
 }