This document summarizes how to use Ruby on Rails with legacy Oracle databases. It discusses using the ruby-oci8 and jruby-oci8 gems to connect to Oracle from Ruby. It also covers using the activerecord-oracle_enhanced-adapter gem to connect to Oracle from Rails. It provides examples of calling PL/SQL functions from Ruby using the ruby-plsql gem and overriding ActiveRecord methods to call custom PL/SQL packages. Finally, it diagrams a typical Rails application architecture when using an Oracle database.