diff --git a/lib/defs.go b/lib/defs.go
new file mode 100644
index 0000000..c3227eb
--- /dev/null
+++ b/lib/defs.go
@@ -0,0 +1,11 @@
+package lib
+
+// Various constants used throughout the tools.
+
+const (
+	// ExitSuccess is the successful exit status.
+	ExitSuccess = 0
+
+	// ExitFailure is the failing exit status.
+	ExitFailure = 1
+)
diff --git a/lib/lib.go b/lib/lib.go
new file mode 100644
index 0000000..42178fc
--- /dev/null
+++ b/lib/lib.go
@@ -0,0 +1,47 @@
+// Package lib contains functions useful for most programs.
+package lib
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+)
+
+var progname = filepath.Base(os.Args[0])
+
+// Warnx displays a formatted error message to standard error, à la
+// warnx(3).
+func Warnx(format string, a ...interface{}) (int, error) {
+	format = fmt.Sprintf("[%s] %s", progname, format)
+	format += "\n"
+	return fmt.Fprintf(os.Stderr, format, a...)
+}
+
+// Warn displays a formatted error message to standard output,
+// appending the error string, à la warn(3).
+func Warn(err error, format string, a ...interface{}) (int, error) {
+	format = fmt.Sprintf("[%s] %s", progname, format)
+	format += ": %v\n"
+	a = append(a, err)
+	return fmt.Fprintf(os.Stderr, format, a...)
+}
+
+// Errx displays a formatted error message to standard error and exits
+// with the status code from `exit`, à la errx(3).
+func Errx(exit int, format string, a ...interface{}) {
+	format = fmt.Sprintf("[%s] %s", progname, format)
+	format += "\n"
+	fmt.Fprintf(os.Stderr, format, a...)
+	os.Exit(exit)
+}
+
+// Err displays a formatting error message to standard error,
+// appending the error string, and exits with the status code from
+// `exit`, à la err(3).
+func Err(exit int, err error, format string, a ...interface{}) {
+	format = fmt.Sprintf("[%s] %s", progname, format)
+	format += ": %v\n"
+	a = append(a, err)
+	fmt.Fprintf(os.Stderr, format, a...)
+	os.Exit(exit)
+}
diff --git a/logging/example/logger.go b/logging/example/logger.go
new file mode 100644
index 0000000..12f083b
--- /dev/null
+++ b/logging/example/logger.go
@@ -0,0 +1,31 @@
+package main
+
+import "github.com/kisom/goutils/logging"
+
+var log = logging.Init()
+var olog = logging.New("subsystem #42", logging.LevelNotice)
+
+func main() {
+	log.Notice("Hello, world.")
+	log.Warning("this program is about to end")
+
+	olog.Print("now online")
+	logging.Suppress("olog")
+	olog.Print("extraneous information")
+
+	logging.Enable("olog")
+	olog.Print("relevant now")
+
+	logging.SuppressAll()
+	log.Alert("screaming into the void")
+	olog.Critical("can anyone hear me?")
+
+	log.Enable()
+	log.Notice("i'm baaack")
+	log.Suppress()
+	log.Warning("but not for long")
+
+	logging.EnableAll()
+	log.Notice("fare thee well")
+	olog.Print("all good journeys must come to an end")
+}
diff --git a/logging/levels.go b/logging/levels.go
new file mode 100644
index 0000000..209cac1
--- /dev/null
+++ b/logging/levels.go
@@ -0,0 +1,200 @@
+package logging
+
+import (
+	"fmt"
+	"os"
+	"time"
+)
+
+// A Level represents a logging level.
+type Level uint8
+
+// The following constants represent logging levels in increasing levels of seriousness.
+const (
+	// LevelDebug are debug output useful during program testing
+	// and debugging.
+	LevelDebug = iota
+
+	// LevelInfo is used for informational messages.
+	LevelInfo
+
+	// LevelNotice is for messages that are normal but
+	// significant.
+	LevelNotice
+
+	// LevelWarning is for messages that are warning conditions:
+	// they're not indicative of a failure, but of a situation
+	// that may lead to a failure later.
+	LevelWarning
+
+	// LevelError is for messages indicating an error of some
+	// kind.
+	LevelError
+
+	// LevelCritical are messages for critical conditions.
+	LevelCritical
+
+	// LevelAlert are for messages indicating that action
+	// must be taken immediately.
+	LevelAlert
+
+	// LevelFatal messages are akin to syslog's LOG_EMERG: the
+	// system is unusable and cannot continue execution.
+	LevelFatal
+)
+
+func writeToOut(level Level) bool {
+	if level < LevelWarning {
+		return true
+	}
+	return false
+}
+
+var levelPrefix = [...]string{
+	LevelDebug:    "[DEBUG] ",
+	LevelInfo:     "[INFO] ",
+	LevelNotice:   "[NOTICE] ",
+	LevelWarning:  "[WARNING] ",
+	LevelError:    "[ERROR] ",
+	LevelCritical: "[CRITICAL] ",
+	LevelAlert:    "[ALERT] ",
+	LevelFatal:    "[FATAL] ",
+}
+
+var DateFormat = "2006-01-02T15:03:04-0700"
+
+func (l *Logger) outputf(level Level, format string, v []interface{}) {
+	if !logConfig.registered[l.domain] {
+		return
+	}
+
+	if level >= l.level {
+		format = fmt.Sprintf("%s %s: %s%s\n",
+			time.Now().Format(DateFormat),
+			l.domain, levelPrefix[level], format)
+		if writeToOut(level) {
+			fmt.Fprintf(l.out, format, v...)
+		} else {
+			fmt.Fprintf(l.err, format, v...)
+		}
+	}
+}
+
+func (l *Logger) output(level Level, v []interface{}) {
+	if !logConfig.registered[l.domain] {
+		return
+	}
+
+	if level >= l.level {
+		format := fmt.Sprintf("%s %s: %s",
+			time.Now().Format(DateFormat),
+			l.domain, levelPrefix[level])
+		if writeToOut(level) {
+			fmt.Fprintf(l.out, format)
+			fmt.Fprintln(l.out, v...)
+		} else {
+			fmt.Fprintf(l.err, format)
+			fmt.Fprintln(l.err, v...)
+		}
+	}
+}
+
+// Fatalf logs a formatted message at the "fatal" level and then exits. The
+// arguments are handled in the same manner as fmt.Printf.
+func (l *Logger) Fatalf(format string, v ...interface{}) {
+	l.outputf(LevelFatal, format, v)
+	os.Exit(1)
+}
+
+// Fatal logs its arguments at the "fatal" level and then exits.
+func (l *Logger) Fatal(v ...interface{}) {
+	l.output(LevelFatal, v)
+	os.Exit(1)
+}
+
+// Alertf logs a formatted message at the "alert" level. The
+// arguments are handled in the same manner as fmt.Printf.
+func (l *Logger) Alertf(format string, v ...interface{}) {
+	l.outputf(LevelAlert, format, v)
+}
+
+// Alert logs its arguments at the "alert" level.
+func (l *Logger) Alert(v ...interface{}) {
+	l.output(LevelAlert, v)
+}
+
+// Criticalf logs a formatted message at the "critical" level. The
+// arguments are handled in the same manner as fmt.Printf.
+func (l *Logger) Criticalf(format string, v ...interface{}) {
+	l.outputf(LevelCritical, format, v)
+}
+
+// Critical logs its arguments at the "critical" level.
+func (l *Logger) Critical(v ...interface{}) {
+	l.output(LevelCritical, v)
+}
+
+// Errorf logs a formatted message at the "error" level. The arguments
+// are handled in the same manner as fmt.Printf.
+func (l *Logger) Errorf(format string, v ...interface{}) {
+	l.outputf(LevelError, format, v)
+}
+
+// Error logs its arguments at the "error" level.
+func (l *Logger) Error(v ...interface{}) {
+	l.output(LevelError, v)
+}
+
+// Warningf logs a formatted message at the "warning" level. The
+// arguments are handled in the same manner as fmt.Printf.
+func (l *Logger) Warningf(format string, v ...interface{}) {
+	l.outputf(LevelWarning, format, v)
+}
+
+// Warning logs its arguments at the "warning" level.
+func (l *Logger) Warning(v ...interface{}) {
+	l.output(LevelWarning, v)
+}
+
+// Noticef logs a formatted message at the "notice" level. The arguments
+// are handled in the same manner as fmt.Printf.
+func (l *Logger) Noticef(format string, v ...interface{}) {
+	l.outputf(LevelNotice, format, v)
+}
+
+// Notice logs its arguments at the "notice" level.
+func (l *Logger) Notice(v ...interface{}) {
+	l.output(LevelNotice, v)
+}
+
+// Infof logs a formatted message at the "info" level. The arguments
+// are handled in the same manner as fmt.Printf.
+func (l *Logger) Infof(format string, v ...interface{}) {
+	l.outputf(LevelInfo, format, v)
+}
+
+// Info logs its arguments at the "info" level.
+func (l *Logger) Info(v ...interface{}) {
+	l.output(LevelInfo, v)
+}
+
+// Debugf logs a formatted message at the "debug" level. The arguments
+// are handled in the same manner as fmt.Printf.
+func (l *Logger) Debugf(format string, v ...interface{}) {
+	l.outputf(LevelDebug, format, v)
+}
+
+// Debug logs its arguments at the "debug" level.
+func (l *Logger) Debug(v ...interface{}) {
+	l.output(LevelDebug, v)
+}
+
+// Printf prints a formatted message at the default level.
+func (l *Logger) Printf(format string, v ...interface{}) {
+	l.outputf(DefaultLevel, format, v)
+}
+
+// Print prints its arguments at the default level.
+func (l *Logger) Print(v ...interface{}) {
+	l.output(DefaultLevel, v)
+}
diff --git a/logging/log.go b/logging/log.go
new file mode 100644
index 0000000..1337eaf
--- /dev/null
+++ b/logging/log.go
@@ -0,0 +1,165 @@
+// Package logging is an adaptation of the CFSSL logging library. It
+// operates on domains, which are components for which logging can be
+// selectively enabled or disabled. It also differentiates between
+// normal messages (which are sent to standard output) and errors,
+// which are sent to standard error.
+package logging
+
+import (
+	"io"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/kisom/goutils/mwc"
+)
+
+var logConfig = struct {
+	registered map[string]bool
+	lock       *sync.Mutex
+}{
+	registered: map[string]bool{},
+	lock:       new(sync.Mutex),
+}
+
+// DefaultLevel defaults to the notice level of logging.
+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)
+}
+
+// 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
+}
+
+// Close closes the log's writers and suppresses the logger.
+func (l *Logger) Close() error {
+	Suppress(l.domain)
+	err := l.out.Close()
+	if err != nil {
+		return nil
+	}
+
+	return l.err.Close()
+}
+
+// Suppress ignores logs from a specific domain.
+func Suppress(domain string) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	logConfig.registered[domain] = false
+}
+
+// SuppressAll suppresses all logging output.
+func SuppressAll() {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	for domain := range logConfig.registered {
+		logConfig.registered[domain] = false
+	}
+}
+
+// Enable enables logs from a specific domain.
+func Enable(domain string) {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	logConfig.registered[domain] = true
+}
+
+// EnableAll enables all domains.
+func EnableAll() {
+	logConfig.lock.Lock()
+	defer logConfig.lock.Unlock()
+	for domain := range logConfig.registered {
+		logConfig.registered[domain] = true
+	}
+}
+
+// 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{
+		domain: domain,
+		level:  level,
+		out:    os.Stdout,
+		err:    os.Stderr,
+	}
+
+	Enable(domain)
+	return l
+}
+
+// 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 NewWriters(domain string, level Level, w, e io.WriteCloser) *Logger {
+	if e == nil {
+		e = w
+	}
+
+	l := &Logger{
+		domain: domain,
+		level:  level,
+		out:    w,
+		err:    e,
+	}
+
+	Enable(domain)
+	return l
+}
+
+// NewFile returns a new logger that opens the files for writing. If
+// multiplex is true, output will be multiplexed to standard output
+// and standard error as well.
+func NewFile(domain string, level Level, outFile, errFile string, multiplex bool) (*Logger, error) {
+	l := &Logger{
+		domain: domain,
+		level:  level,
+	}
+
+	var err error
+	l.out, err = os.OpenFile(outFile, os.O_APPEND|os.O_CREATE, 0644)
+	if err != nil {
+		return nil, err
+	}
+
+	l.err, err = os.OpenFile(errFile, os.O_APPEND|os.O_CREATE, 0644)
+	if err != nil {
+		return nil, err
+	}
+
+	if multiplex {
+		l.out = mwc.MultiWriteCloser(l.out, os.Stdout)
+		l.err = mwc.MultiWriteCloser(l.err, os.Stderr)
+	}
+
+	Enable(domain)
+	return l, nil
+}
+
+// Enable allows output from the logger.
+func (l *Logger) Enable() {
+	Enable(l.domain)
+}
+
+// Suppress ignores output from the logger.
+func (l *Logger) Suppress() {
+	Suppress(l.domain)
+}
+
+// Domain returns the domain of the logger.
+func (l *Logger) Domain() string {
+	return l.domain
+}
+
+// SetLevel changes the level of the logger.
+func (l *Logger) SetLevel(level Level) {
+	l.level = level
+}
diff --git a/mwc/mwc.go b/mwc/mwc.go
new file mode 100644
index 0000000..64a023c
--- /dev/null
+++ b/mwc/mwc.go
@@ -0,0 +1,42 @@
+// Package mwc implements MultiWriteClosers.
+package mwc
+
+import "io"
+
+type mwc struct {
+	wcs []io.WriteCloser
+}
+
+// Write implements the Writer interface.
+func (t *mwc) Write(p []byte) (n int, err error) {
+	for _, w := range t.wcs {
+		n, err = w.Write(p)
+		if err != nil {
+			return
+		}
+		if n != len(p) {
+			err = io.ErrShortWrite
+			return
+		}
+	}
+	return len(p), nil
+}
+
+// Close implements the Closer interface.
+func (t *mwc) Close() error {
+	for _, wc := range t.wcs {
+		err := wc.Close()
+		if err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// MultiWriteClose creates a WriteCloser that duplicates its writes to
+// all the provided writers, similar to the Unix tee(1) command.
+func MultiWriteCloser(wc ...io.WriteCloser) io.WriteCloser {
+	wcs := make([]io.WriteCloser, len(wc))
+	copy(wcs, wc)
+	return &mwc{wcs}
+}