diff --git a/README.md b/README.md
index 335364f..8843268 100644
--- a/README.md
+++ b/README.md
@@ -7,7 +7,7 @@ variety of languages and technologies. These are things that don't really
 warrant a full blog post. These are mostly things I learn by pairing with
 smart people at [Hashrocket](http://hashrocket.com/).
 
-_499 TILs and counting..._
+_500 TILs and counting..._
 
 ---
 
@@ -110,6 +110,7 @@ _499 TILs and counting..._
 - [Run ExUnit Tests In A Deterministic Order](elixir/run-exunit-tests-in-a-deterministic-order.md)
 - [Same Functions Should Be Grouped Together](elixir/same-functions-should-be-grouped-together.md)
 - [String Interpolation With Just About Anything](elixir/string-interpolation-with-just-about-anything.md)
+- [Unique Indexes With Ecto](elixir/unique-indexes-with-ecto.md)
 - [Updating Values In A Map](elixir/updating-values-in-a-map.md)
 - [Virtual Fields With Ecto Schemas](elixir/virtual-fields-with-ecto-schemas.md)
 - [Word Lists For Atoms](elixir/word-lists-for-atoms.md)
diff --git a/elixir/unique-indexes-with-ecto.md b/elixir/unique-indexes-with-ecto.md
new file mode 100644
index 0000000..15baf4b
--- /dev/null
+++ b/elixir/unique-indexes-with-ecto.md
@@ -0,0 +1,21 @@
+# Unique Indexes With Ecto
+
+You can create a unique index in a migration for one or more columns using
+the [`unique_index/3`] function.
+
+For example, if you are creating a join table for `followers` and want to
+ensure that duplicate _follower_ entries are prevented, you may want to
+include a unique index like so:
+
+```elixir
+create table(:followers) do
+  add :followed_user, references(:users), null: false
+  add :following_user, references(:users), null: false
+end
+
+create unique_index(:followers, [:followed_user, :following_user])
+```
+
+Keep in mind that `unique_index/3` is a shorthand for
+[`index/3`](https://hexdocs.pm/ecto/Ecto.Migration.html#index/3) when you
+set `unique: true`.