I've posted a Gist showing an example of how to import sub-templates into ERB files.
Many people are familiar with the concept of "partials" in (RubyOn)Rails. This subtemplating ability is part of ActionView and is not part of ERB itself (the templating language included in every Ruby install).
There are many times when you may want to have the functionality of "partials" without all of the overhead of including ActionView into your code. At BlueHead Publishing, we are using this in our bookshop software, to have a templating structure for author's books.
The code example below shows how to create a method called import() which you can use in your ERB to import subtemplates (other .erb files) into your master ERB file, reproducing some of the "partials" functionality you may be used to in Rails.