diff --git a/.adr-dir b/.adr-dir
new file mode 100644
index 0000000..0a5ca20
--- /dev/null
+++ b/.adr-dir
@@ -0,0 +1 @@
+adr
diff --git a/CHANGELOG.md b/CHANGELOG.md
index aae0911..47d2309 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## [Unreleased]
 
+### Added
+
+- Added Architecture Decision Records (ADRs) to document architectural decisions
+
 ### Fixed
 
 - Fixed YARD example rendering issues in `InvalidKeyFormatError#initialize`, `InvalidKeyLengthError#initialize`,
diff --git a/adr/0001-record-architecture-decisions.md b/adr/0001-record-architecture-decisions.md
new file mode 100644
index 0000000..e596e35
--- /dev/null
+++ b/adr/0001-record-architecture-decisions.md
@@ -0,0 +1,19 @@
+# 1. Record architecture decisions
+
+Date: 2024-03-13
+
+## Status
+
+Accepted
+
+## Context
+
+We need to record the architectural decisions made on this project.
+
+## Decision
+
+We will use Architecture Decision Records, as [described by Michael Nygard](http://thinkrelevance.com/blog/2011/11/15/documenting-architecture-decisions).
+
+## Consequences
+
+See Michael Nygard's article, linked above. For a lightweight ADR toolset, see Nat Pryce's [adr-tools](https://github.com/npryce/adr-tools).