One great starting point is ActiveSupport, specifically the core extensions: http://github.com/rails/rails/tree/master/activesupport/lib/active_support/core_ex

One great starting point is ActiveSupport, specifically the core extensions: http://github.com/rails/rails/tree/master/activesupport/lib/active_support/core_ext/ http://github.com/rails/rails/tree/master/activesupport/lib/... Though this library isn't really Rails-specific, it has a bunch of self-contained ruby files, good to learn about the style of doing things elsewhere in rails. Examples: Array#uniq_by, String#pluralize, Numeric#hours, etc. The Rails router, while considerably more complex than ActiveSupport, is also a self-contained chunk of code you can read: http://github.com/rails/rails/tree/master/actionpack/lib/action_dispatch/routing/ http://github.com/rails/rails/tree/master/actionpack/lib/act... Also: When reading Rails code (or any ruby library's code, for that matter), I've found that reading the specs first is very effective.