diff --git a/README.md b/README.md
index 035eeda..a06f914 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ if err != nil {
 }
 
 // Write a file and track it with `git add`.
-err = ioutil.WriteFile("foo.txt", []byte("Hello, World!\n"), 0666)
+err = os.WriteFile("foo.txt", []byte("Hello, World!\n"), 0o666)
 if err != nil {
   return err
 }
diff --git a/cat_test.go b/cat_test.go
index de15abe..e25250d 100644
--- a/cat_test.go
+++ b/cat_test.go
@@ -16,7 +16,7 @@ package git
 
 import (
 	"context"
-	"io/ioutil"
+	"io"
 	"strings"
 	"testing"
 
@@ -76,7 +76,7 @@ func TestCat(t *testing.T) {
 			if err != nil {
 				t.Fatal("Cat error:", err)
 			}
-			got, err := ioutil.ReadAll(r)
+			got, err := io.ReadAll(r)
 			if string(got) != test.want {
 				t.Errorf("read content = %q; want %q", got, test.want)
 			}
diff --git a/example_test.go b/example_test.go
index 7b8144a..30cc6f4 100644
--- a/example_test.go
+++ b/example_test.go
@@ -19,7 +19,8 @@ package git_test
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
+
+	"os"
 
 	"gg-scm.io/pkg/git"
 )
@@ -90,7 +91,7 @@ func ExampleGit_Commit() {
 	}
 
 	// Write a file and track it with `git add`.
-	err = ioutil.WriteFile("foo.txt", []byte("Hello, World!\n"), 0666)
+	err = os.WriteFile("foo.txt", []byte("Hello, World!\n"), 0o666)
 	if err != nil {
 		// handle error
 	}
diff --git a/git_test.go b/git_test.go
index 656e3c6..8ef576f 100644
--- a/git_test.go
+++ b/git_test.go
@@ -16,7 +16,6 @@ package git
 
 import (
 	"context"
-	"io/ioutil"
 	"os"
 	"os/exec"
 	"path/filepath"
@@ -58,15 +57,7 @@ func TestLocalCommand(t *testing.T) {
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
 			ctx := context.Background()
-			dir, err := ioutil.TempDir("", "gg_gittool_test")
-			if err != nil {
-				t.Fatal(err)
-			}
-			defer func() {
-				if err := os.Remove(dir); err != nil {
-					t.Error("cleaning up directory:", err)
-				}
-			}()
+			dir := t.TempDir()
 			var hookArgs []string
 			var env []string
 			if test.env != nil {
@@ -221,7 +212,7 @@ type testEnv struct {
 }
 
 func newTestEnv(ctx context.Context, gitExe string) (*testEnv, error) {
-	topPath, err := ioutil.TempDir("", "gg_git_test")
+	topPath, err := os.MkdirTemp("", "gg_git_test")
 	if err != nil {
 		return nil, err
 	}
diff --git a/internal/filesystem/filesystem.go b/internal/filesystem/filesystem.go
index 0fc980c..8833266 100644
--- a/internal/filesystem/filesystem.go
+++ b/internal/filesystem/filesystem.go
@@ -19,7 +19,6 @@ package filesystem
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -125,17 +124,17 @@ func (dir Dir) Apply(ops ...Operation) error {
 		case nop:
 			// Do nothing.
 		case opWrite:
-			if err := os.MkdirAll(filepath.Dir(p), 0777); err != nil {
+			if err := os.MkdirAll(filepath.Dir(p), 0o777); err != nil {
 				return err
 			}
-			if err := ioutil.WriteFile(p, []byte(o.arg), 0666); err != nil {
+			if err := os.WriteFile(p, []byte(o.arg), 0o666); err != nil {
 				return err
 			}
 		case opMkdir:
-			if err := os.MkdirAll(filepath.Dir(p), 0777); err != nil {
+			if err := os.MkdirAll(filepath.Dir(p), 0o777); err != nil {
 				return err
 			}
-			if err := os.Mkdir(p, 0777); err != nil {
+			if err := os.Mkdir(p, 0o777); err != nil {
 				return err
 			}
 		case opRemove:
diff --git a/internal/filesystem/filesystem_test.go b/internal/filesystem/filesystem_test.go
index 559eeaf..aa8d5e5 100644
--- a/internal/filesystem/filesystem_test.go
+++ b/internal/filesystem/filesystem_test.go
@@ -15,7 +15,6 @@
 package filesystem
 
 import (
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -24,21 +23,13 @@ import (
 func TestApply(t *testing.T) {
 	t.Run("Write/Top", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
+		dir := t.TempDir()
 		const wantContent = "Hello, World!\n"
-		err = Dir(dir).Apply(Write("foo.txt", wantContent))
+		err := Dir(dir).Apply(Write("foo.txt", wantContent))
 		if err != nil {
 			t.Error("Apply(...) =", err)
 		}
-		got, err := ioutil.ReadFile(filepath.Join(dir, "foo.txt"))
+		got, err := os.ReadFile(filepath.Join(dir, "foo.txt"))
 		if err != nil {
 			t.Error(err)
 		} else if string(got) != wantContent {
@@ -47,21 +38,13 @@ func TestApply(t *testing.T) {
 	})
 	t.Run("Write/SubDir", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
+		dir := t.TempDir()
 		const wantContent = "Hello, World!\n"
-		err = Dir(dir).Apply(Write("foo/bar/baz.txt", wantContent))
+		err := Dir(dir).Apply(Write("foo/bar/baz.txt", wantContent))
 		if err != nil {
 			t.Error("Apply(...) =", err)
 		}
-		got, err := ioutil.ReadFile(filepath.Join(dir, "foo", "bar", "baz.txt"))
+		got, err := os.ReadFile(filepath.Join(dir, "foo", "bar", "baz.txt"))
 		if err != nil {
 			t.Error(err)
 		} else if string(got) != wantContent {
@@ -70,21 +53,13 @@ func TestApply(t *testing.T) {
 	})
 	t.Run("Mkdir/New", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
-		err = Dir(dir).Apply(Mkdir("foo/bar/baz"))
+		dir := t.TempDir()
+		err := Dir(dir).Apply(Mkdir("foo/bar/baz"))
 		if err != nil {
 			t.Error("Apply(...) =", err)
 		}
 		madeDir := filepath.Join(dir, "foo", "bar", "baz")
-		got, err := ioutil.ReadDir(madeDir)
+		got, err := os.ReadDir(madeDir)
 		if err != nil {
 			t.Error(err)
 		} else if len(got) > 0 {
@@ -93,46 +68,30 @@ func TestApply(t *testing.T) {
 	})
 	t.Run("Mkdir/Exists", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
+		dir := t.TempDir()
 		if err := os.MkdirAll(filepath.Join(dir, "foo", "bar"), 0777); err != nil {
 			t.Fatal(err)
 		}
-		err = Dir(dir).Apply(Mkdir("foo/bar"))
+		err := Dir(dir).Apply(Mkdir("foo/bar"))
 		if err == nil {
 			t.Error("Apply(...) = nil; want error")
 		}
 	})
 	t.Run("Remove/Exists", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
+		dir := t.TempDir()
 		parent := filepath.Join(dir, "foo")
 		if err := os.Mkdir(parent, 0777); err != nil {
 			t.Fatal(err)
 		}
-		if err := ioutil.WriteFile(filepath.Join(parent, "bar.txt"), []byte("sup"), 0666); err != nil {
+		if err := os.WriteFile(filepath.Join(parent, "bar.txt"), []byte("sup"), 0o666); err != nil {
 			t.Fatal(err)
 		}
-		err = Dir(dir).Apply(Remove("foo/bar.txt"))
+		err := Dir(dir).Apply(Remove("foo/bar.txt"))
 		if err != nil {
 			t.Error("Apply(...) =", err)
 		}
-		got, err := ioutil.ReadDir(parent)
+		got, err := os.ReadDir(parent)
 		if err != nil {
 			t.Error(err)
 		} else if len(got) > 0 {
@@ -141,24 +100,16 @@ func TestApply(t *testing.T) {
 	})
 	t.Run("Remove/DoesNotExist", func(t *testing.T) {
 		t.Parallel()
-		dir, err := ioutil.TempDir("", "gg_filesystem")
-		if err != nil {
-			t.Fatal(err)
-		}
-		defer func() {
-			if err := os.RemoveAll(dir); err != nil {
-				t.Error("clean up temp dir:", err)
-			}
-		}()
+		dir := t.TempDir()
 		parent := filepath.Join(dir, "foo")
 		if err := os.Mkdir(parent, 0777); err != nil {
 			t.Fatal(err)
 		}
-		err = Dir(dir).Apply(Remove("foo/bar.txt"))
+		err := Dir(dir).Apply(Remove("foo/bar.txt"))
 		if err == nil {
 			t.Error("Apply(...) = nil; want error")
 		}
-		got, err := ioutil.ReadDir(parent)
+		got, err := os.ReadDir(parent)
 		if err != nil {
 			t.Error(err)
 		} else if len(got) > 0 {
@@ -168,21 +119,13 @@ func TestApply(t *testing.T) {
 }
 
 func TestReadFile(t *testing.T) {
-	dir, err := ioutil.TempDir("", "gg_filesystem")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer func() {
-		if err := os.RemoveAll(dir); err != nil {
-			t.Error("clean up temp dir:", err)
-		}
-	}()
+	dir := t.TempDir()
 	parent := filepath.Join(dir, "foo")
 	if err := os.Mkdir(parent, 0777); err != nil {
 		t.Fatal(err)
 	}
 	const want = "Hello, World!\n"
-	if err := ioutil.WriteFile(filepath.Join(parent, "bar.txt"), []byte(want), 0666); err != nil {
+	if err := os.WriteFile(filepath.Join(parent, "bar.txt"), []byte(want), 0666); err != nil {
 		t.Fatal(err)
 	}
 	got, err := Dir(dir).ReadFile("foo/bar.txt")
diff --git a/object/tree_test.go b/object/tree_test.go
index 309aa61..4dbf51c 100644
--- a/object/tree_test.go
+++ b/object/tree_test.go
@@ -19,7 +19,6 @@ package object
 import (
 	"encoding"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -142,7 +141,7 @@ var treeTests = []struct {
 func TestParseTree(t *testing.T) {
 	for _, test := range treeTests {
 		t.Run(test.name, func(t *testing.T) {
-			src, err := ioutil.ReadFile(filepath.Join("testdata", fmt.Sprintf("tree-%x", test.id)))
+			src, err := os.ReadFile(filepath.Join("testdata", fmt.Sprintf("tree-%x", test.id)))
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -161,7 +160,7 @@ func TestParseTree(t *testing.T) {
 func TestTreeMarshalBinary(t *testing.T) {
 	for _, test := range treeTests {
 		t.Run(test.name, func(t *testing.T) {
-			want, err := ioutil.ReadFile(filepath.Join("testdata", fmt.Sprintf("tree-%x", test.id)))
+			want, err := os.ReadFile(filepath.Join("testdata", fmt.Sprintf("tree-%x", test.id)))
 			if err != nil {
 				t.Fatal(err)
 			}
diff --git a/packfile/buildindex.go b/packfile/buildindex.go
index e75b944..71298b6 100644
--- a/packfile/buildindex.go
+++ b/packfile/buildindex.go
@@ -24,7 +24,6 @@ import (
 	"hash"
 	"hash/crc32"
 	"io"
-	"io/ioutil"
 	"sort"
 	"sync"
 
@@ -203,7 +202,7 @@ func baseIndexPass(r *byteReaderCounter, nobjs uint32) (*baseIndex, error) {
 		objType := hdr.Type.NonDelta()
 		if objType == "" {
 			// Deltified object.
-			size, err := io.Copy(ioutil.Discard, z)
+			size, err := io.Copy(io.Discard, z)
 			if err != nil {
 				return nil, err
 			}
diff --git a/packfile/client/http.go b/packfile/client/http.go
index 2e2df84..f4af8e8 100644
--- a/packfile/client/http.go
+++ b/packfile/client/http.go
@@ -22,7 +22,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/url"
 	"strings"
@@ -141,7 +140,7 @@ func (r *httpRemote) uploadPack(ctx context.Context, extraParams string, request
 			contentTypeHeader: {"application/x-git-upload-pack-request"},
 			gitProtocolHeader: {extraParams},
 		},
-		Body: ioutil.NopCloser(request),
+		Body: io.NopCloser(request),
 	})
 	if err != nil {
 		return nil, err
diff --git a/packfile/client/pull_test.go b/packfile/client/pull_test.go
index 39359c2..54ffb01 100644
--- a/packfile/client/pull_test.go
+++ b/packfile/client/pull_test.go
@@ -25,7 +25,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"net/http"
 	"net/http/cgi"
 	"net/http/httptest"
@@ -281,7 +280,7 @@ func initPullTestRepository(ctx context.Context, g *git.Git, dir string) (*pullT
 	}
 	const filename1 = "1.txt"
 	const fileContent = "Hello, World!\n"
-	err = ioutil.WriteFile(filepath.Join(dir, filename1), []byte(fileContent), 0o666)
+	err = os.WriteFile(filepath.Join(dir, filename1), []byte(fileContent), 0o666)
 	if err != nil {
 		return nil, err
 	}
@@ -307,7 +306,7 @@ func initPullTestRepository(ctx context.Context, g *git.Git, dir string) (*pullT
 	}
 
 	const filename2 = "2.txt"
-	err = ioutil.WriteFile(filepath.Join(dir, filename2), []byte(fileContent), 0o666)
+	err = os.WriteFile(filepath.Join(dir, filename2), []byte(fileContent), 0o666)
 	if err != nil {
 		return nil, err
 	}
@@ -482,7 +481,7 @@ func serveHTTPRepository(gitExe string, dir string) *httptest.Server {
 			// Go's net/http/cgi server doesn't support chunked encoding, which is
 			// a non-standard CGI feature that Apache supports. https://golang.org/issue/5613
 			// We're okay with a really inefficient implementation for tests.
-			bodyFile, err := ioutil.TempFile("", "git-server-body")
+			bodyFile, err := os.CreateTemp("", "git-server-body")
 			if err != nil {
 				http.Error(w, err.Error(), http.StatusInternalServerError)
 				return
diff --git a/packfile/delta.go b/packfile/delta.go
index 9c6c706..912f619 100644
--- a/packfile/delta.go
+++ b/packfile/delta.go
@@ -22,7 +22,6 @@ import (
 	"encoding/binary"
 	"fmt"
 	"io"
-	"io/ioutil"
 
 	"gg-scm.io/pkg/git/object"
 )
@@ -172,7 +171,7 @@ func DeltaObjectSize(delta ByteReader) (int64, error) {
 		case instruction != 0:
 			// Add new data
 			n += int64(instruction)
-			if err := copyN(ioutil.Discard, delta, int64(instruction)); err != nil {
+			if err := copyN(io.Discard, delta, int64(instruction)); err != nil {
 				return 0, fmt.Errorf("calculate delta object size: %w", err)
 			}
 		default:
diff --git a/packfile/index.go b/packfile/index.go
index 7130951..7a94d75 100644
--- a/packfile/index.go
+++ b/packfile/index.go
@@ -21,7 +21,6 @@ import (
 	"crypto/sha1"
 	"fmt"
 	"io"
-	"io/ioutil"
 	"sort"
 
 	"gg-scm.io/pkg/git/githash"
@@ -213,7 +212,7 @@ func readIndexV1(r io.Reader) (*Index, error) {
 const fanOutEntryCount = 256
 
 func readIndexObjectCount(r io.Reader) (uint32, error) {
-	if _, err := io.CopyN(ioutil.Discard, r, (fanOutEntryCount-1)*4); err != nil {
+	if _, err := io.CopyN(io.Discard, r, (fanOutEntryCount-1)*4); err != nil {
 		return 0, fmt.Errorf("fanout table: %w", err)
 	}
 	var raw [4]byte
diff --git a/packfile/index_test.go b/packfile/index_test.go
index d896f5f..e51d115 100644
--- a/packfile/index_test.go
+++ b/packfile/index_test.go
@@ -19,7 +19,6 @@ package packfile
 import (
 	"bytes"
 	"encoding"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -118,7 +117,7 @@ func TestIndexEncodeV1(t *testing.T) {
 			continue
 		}
 		t.Run(test.name, func(t *testing.T) {
-			want, err := ioutil.ReadFile(filepath.Join("testdata", test.name+".idx1"))
+			want, err := os.ReadFile(filepath.Join("testdata", test.name+".idx1"))
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -133,7 +132,7 @@ func TestIndexEncodeV1(t *testing.T) {
 	}
 
 	t.Run("Nil", func(t *testing.T) {
-		want, err := ioutil.ReadFile(filepath.Join("testdata", "Empty.idx1"))
+		want, err := os.ReadFile(filepath.Join("testdata", "Empty.idx1"))
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -153,7 +152,7 @@ func TestIndexEncodeV2(t *testing.T) {
 			continue
 		}
 		t.Run(test.name, func(t *testing.T) {
-			want, err := ioutil.ReadFile(filepath.Join("testdata", test.name+".idx2"))
+			want, err := os.ReadFile(filepath.Join("testdata", test.name+".idx2"))
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -168,7 +167,7 @@ func TestIndexEncodeV2(t *testing.T) {
 	}
 
 	t.Run("BigOffset", func(t *testing.T) {
-		want, err := ioutil.ReadFile(filepath.Join("testdata", "BigOffset.idx2"))
+		want, err := os.ReadFile(filepath.Join("testdata", "BigOffset.idx2"))
 		if err != nil {
 			t.Fatal(err)
 		}
@@ -182,7 +181,7 @@ func TestIndexEncodeV2(t *testing.T) {
 	})
 
 	t.Run("Nil", func(t *testing.T) {
-		want, err := ioutil.ReadFile(filepath.Join("testdata", "Empty.idx2"))
+		want, err := os.ReadFile(filepath.Join("testdata", "Empty.idx2"))
 		if err != nil {
 			t.Fatal(err)
 		}
diff --git a/packfile/reader.go b/packfile/reader.go
index df64ed6..194f820 100644
--- a/packfile/reader.go
+++ b/packfile/reader.go
@@ -22,7 +22,6 @@ import (
 	"errors"
 	"fmt"
 	"io"
-	"io/ioutil"
 
 	"gg-scm.io/pkg/git/githash"
 	"gg-scm.io/pkg/git/object"
@@ -89,7 +88,7 @@ func (r *Reader) Next() (*Header, error) {
 		return nil, err
 	}
 	if r.dataReader != nil {
-		n, err := io.Copy(ioutil.Discard, r.dataReader)
+		n, err := io.Copy(io.Discard, r.dataReader)
 		if err != nil {
 			return nil, fmt.Errorf("packfile: advance to next object: %w", err)
 		}
@@ -104,7 +103,7 @@ func (r *Reader) Next() (*Header, error) {
 	if r.nobjs == 0 {
 		// Consume trailing checksum.
 		// TODO(someday): Verify integrity. This is a SHA-1 hash.
-		if _, err := io.CopyN(ioutil.Discard, &r.r, githash.SHA1Size); err != nil {
+		if _, err := io.CopyN(io.Discard, &r.r, githash.SHA1Size); err != nil {
 			return nil, fmt.Errorf("packfile: read trailing checksum: %w", err)
 		}
 		return nil, io.EOF
diff --git a/packfile/reader_test.go b/packfile/reader_test.go
index c051ab7..f8101d3 100644
--- a/packfile/reader_test.go
+++ b/packfile/reader_test.go
@@ -21,7 +21,6 @@ import (
 	"bytes"
 	"errors"
 	"io"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"testing"
@@ -272,7 +271,7 @@ func readAll(br ByteReader) ([]unpackedObject, error) {
 			}
 			return got, err
 		}
-		data, err := ioutil.ReadAll(r)
+		data, err := io.ReadAll(r)
 		got = append(got, unpackedObject{
 			Header: hdr,
 			Data:   data,
@@ -314,7 +313,7 @@ func hashLiteral(s string) githash.SHA1 {
 }
 
 func BenchmarkReader(b *testing.B) {
-	data, err := ioutil.ReadFile(filepath.Join("testdata", "FirstCommit.pack"))
+	data, err := os.ReadFile(filepath.Join("testdata", "FirstCommit.pack"))
 	if err != nil {
 		b.Fatal(err)
 	}
@@ -332,7 +331,7 @@ func BenchmarkReader(b *testing.B) {
 		if err != nil {
 			b.Fatal(err)
 		}
-		if _, err := io.Copy(ioutil.Discard, r); err != nil {
+		if _, err := io.Copy(io.Discard, r); err != nil {
 			b.Fatal(err)
 		}
 	}
diff --git a/packfile/writer_test.go b/packfile/writer_test.go
index 7d1d669..ef0ef4e 100644
--- a/packfile/writer_test.go
+++ b/packfile/writer_test.go
@@ -20,7 +20,6 @@ import (
 	"bytes"
 	"encoding/binary"
 	"io"
-	"io/ioutil"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -76,7 +75,7 @@ func TestWriter(t *testing.T) {
 	}
 
 	t.Run("TooLong", func(t *testing.T) {
-		w := NewWriter(ioutil.Discard, 1)
+		w := NewWriter(io.Discard, 1)
 		const blobContent = "Hi"
 		_, err := w.WriteHeader(&Header{
 			Type: Blob,
@@ -93,7 +92,7 @@ func TestWriter(t *testing.T) {
 	})
 
 	t.Run("TooShort", func(t *testing.T) {
-		w := NewWriter(ioutil.Discard, 1)
+		w := NewWriter(io.Discard, 1)
 		const blobContent = "Hello"
 		_, err := w.WriteHeader(&Header{
 			Type: Blob,