diff --git a/README.md b/README.md
index 8e85f41..479b81d 100644
--- a/README.md
+++ b/README.md
@@ -10,7 +10,7 @@ pairing with smart people at Hashrocket.
 
 For a steady stream of TILs, [sign up for my newsletter](https://crafty-builder-6996.ck.page/e169c61186).
 
-_1654 TILs and counting..._
+_1655 TILs and counting..._
 
 See some of the other learning resources I work on:
 - [Get Started with Vimium](https://egghead.io/courses/get-started-with-vimium~3t5f7)
@@ -1093,6 +1093,7 @@ If you've learned something here, support my efforts writing daily TILs by
 - [Mock Rails Environment With An Inquiry Instance](rails/mock-rails-environment-with-an-inquiry-instance.md)
 - [Order Matters For `rescue_from` Blocks](rails/order-matters-for-rescue-from-blocks.md)
 - [Override Text Displayed By Form Label](rails/override-text-displayed-by-form-label.md)
+- [Parameterize A String With Underscores](rails/parameterize-a-string-with-underscores.md)
 - [Params Includes Submission Button Info](rails/params-includes-submission-button-info.md)
 - [Params Is A Hash With Indifferent Access](rails/params-is-a-hash-with-indifferent-access.md)
 - [Parse Query Params From A URL](rails/parse-query-params-from-a-url.md)
diff --git a/rails/parameterize-a-string-with-underscores.md b/rails/parameterize-a-string-with-underscores.md
new file mode 100644
index 0000000..1c83fb5
--- /dev/null
+++ b/rails/parameterize-a-string-with-underscores.md
@@ -0,0 +1,40 @@
+# Parameterize A String With Underscores
+
+I have human-readable status strings that I'm working with like `In progress`,
+`Pending approval`, and `Completed`. I need to deterministically turn those
+into parameterized values that I can compare. That is, I want them lowercased
+and separated by underscores instead of spaces.
+
+The `ActiveSupport` `#parameterize` method, as is, gets me pretty close.
+
+```ruby
+> statuses = [
+  "In progress",
+  "Pending approval",
+  "Completed"
+]
+
+> statuses.map(&:parameterize)
+=> [
+  "in-progress",
+  "pending-approval",
+  "completed"
+]
+```
+
+Those are separated by dashes though. Fortunately, `parameterize` takes a
+`separator` option that we can use to verride what character is used to
+separate words. Let's use an underscore (`_`).
+
+```ruby
+> statuses.map { |str| str.parameterize(separator: '_') }
+=> [
+  "in_progress",
+  "pending_approval",
+  "completed"
+]
+```
+
+See the [`#paramterize`
+docs](https://api.rubyonrails.org/classes/ActiveSupport/Inflector.html#method-i-parameterize)
+for more details.