diff --git a/LICENSE.txt b/LICENSE.txt
deleted file mode 100644
index 4a92e28..0000000
--- a/LICENSE.txt
+++ /dev/null
@@ -1,15 +0,0 @@
-ISC License
-
-Copyright 2024 Brandon Dyck
-
-Permission to use, copy, modify, and/or distribute this software for any purpose
- with or without fee is hereby granted, provided that the above copyright notice
-and this permission notice appear in all copies.
-
-THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH
-REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND
-FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
-INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
-OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
-TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
-THIS SOFTWARE.
\ No newline at end of file
diff --git a/TODO.txt b/TODO.txt
index 7e001b8..8fb51d9 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -3,5 +3,4 @@ Think about not requiring so much Pos() when making messages
 Rename Seq2 to Seq
 Document Seq
 Should MakeState be private now that there's Run?
-Add SPDX tags
 What's Megaparsec got that we ain't got?
diff --git a/UNLICENSE b/UNLICENSE
new file mode 100644
index 0000000..b3dbff0
--- /dev/null
+++ b/UNLICENSE
@@ -0,0 +1,22 @@
+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
+OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+OTHER DEALINGS IN THE SOFTWARE.
diff --git a/bind.go b/bind.go
index aea40c6..734ebb3 100644
--- a/bind.go
+++ b/bind.go
@@ -1,5 +1,7 @@
 // GENERATED FILE. DO NOT EDIT.
 
+// SPDX-License-Identifier: Unlicense
+
 package gigaparsec
 
 // Bind combines p with a parser created by f that depends on p's result value.
diff --git a/bytes/regexp.go b/bytes/regexp.go
index aec7c53..8b7a762 100644
--- a/bytes/regexp.go
+++ b/bytes/regexp.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package bytes
 
 import (
diff --git a/bytes/regexp_test.go b/bytes/regexp_test.go
index 3f96828..6e9640f 100644
--- a/bytes/regexp_test.go
+++ b/bytes/regexp_test.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package bytes_test
 
 import (
diff --git a/cursor/cursor.go b/cursor/cursor.go
index 7a765fd..446cdaa 100644
--- a/cursor/cursor.go
+++ b/cursor/cursor.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package cursor
 
 import (
diff --git a/cursor/cursor_test.go b/cursor/cursor_test.go
index da406e0..7b4c422 100644
--- a/cursor/cursor_test.go
+++ b/cursor/cursor_test.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package cursor_test
 
 import (
diff --git a/cursor/helper.go b/cursor/helper.go
index 715317c..80b87b9 100644
--- a/cursor/helper.go
+++ b/cursor/helper.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package cursor
 
 import (
diff --git a/cursor/helper_test.go b/cursor/helper_test.go
index a3fd2a0..3a32af6 100644
--- a/cursor/helper_test.go
+++ b/cursor/helper_test.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package cursor_test
 
 import "testing"
diff --git a/gigaparsec.go b/gigaparsec.go
index 3fb5f5b..a199d2c 100644
--- a/gigaparsec.go
+++ b/gigaparsec.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package gigaparsec
 
 //go:generate go run ./internal/bindgen -bindpath bind.go -seqpath seq.go -max 5 -pkg gigaparsec
diff --git a/internal/bindgen/bind.go.tmpl b/internal/bindgen/bind.go.tmpl
index 5566af3..ed4191e 100644
--- a/internal/bindgen/bind.go.tmpl
+++ b/internal/bindgen/bind.go.tmpl
@@ -1,3 +1,5 @@
+{{/* SPDX-License-Identifier: Unlicense */ -}}
+
 {{define "fparams" -}}
 {{with $max := .}}{{range .Count}}	f{{.}} func(T{{.}}) Parser[In, {{if eq . $max}}Out{{else}}T{{.Next}}{{end}}],
 {{end}}{{end}}{{end -}}
@@ -31,6 +33,8 @@ func Bind{{.}}[In, Out{{range .Count}}, T{{.}}{{end}} any](
 
 // GENERATED FILE. DO NOT EDIT.
 
+// SPDX-License-Identifier: Unlicense
+
 package {{.Package}}
 {{range .Count}}
 {{template "func" .}}
diff --git a/internal/bindgen/bindgen.go b/internal/bindgen/bindgen.go
index e422c73..6c4d036 100644
--- a/internal/bindgen/bindgen.go
+++ b/internal/bindgen/bindgen.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package main
 
 import (
diff --git a/internal/bindgen/seq.go.tmpl b/internal/bindgen/seq.go.tmpl
index a8b1fa6..b626d91 100644
--- a/internal/bindgen/seq.go.tmpl
+++ b/internal/bindgen/seq.go.tmpl
@@ -1,3 +1,5 @@
+{{/* SPDX-License-Identifier: Unlicense */ -}}
+
 {{define "func"}}{{if gt . 1 -}}
 func Seq{{.}}[In, Out{{range .Count}}, T{{.}}{{end}} any](
 	{{- range .Count}}
@@ -28,6 +30,8 @@ func Seq{{.}}[In, Out{{range .Count}}, T{{.}}{{end}} any](
 
 // GENERATED FILE. DO NOT EDIT.
 
+// SPDX-License-Identifier: Unlicense
+
 package {{.Package}}
 {{range .Count}}{{template "func" .}}
 
diff --git a/parser_test.go b/parser_test.go
index 788675d..088dda0 100644
--- a/parser_test.go
+++ b/parser_test.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package gigaparsec_test
 
 import (
diff --git a/seq.go b/seq.go
index 6296d36..7319041 100644
--- a/seq.go
+++ b/seq.go
@@ -1,5 +1,7 @@
 // GENERATED FILE. DO NOT EDIT.
 
+// SPDX-License-Identifier: Unlicense
+
 package gigaparsec
 
 func Seq2[In, Out, T, T2 any](
diff --git a/test/generator/gen.go b/test/generator/gen.go
index b0d4010..352d06c 100644
--- a/test/generator/gen.go
+++ b/test/generator/gen.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 package generator
 
 import (
diff --git a/test/readerat.go b/test/readerat.go
index d61be8d..502cb51 100644
--- a/test/readerat.go
+++ b/test/readerat.go
@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Unlicense
+
 // Package test contains helpers for testing parsers.
 package test