A very common use case for Module#prepend is for mixins that want to decorate methods. For example, say I have a class that can process stuff, and a mixin that

A very common use case for Module#prepend is for mixins that want to decorate methods. For example, say I have a class that can process stuff, and a mixin that attempts to log calls to the #process method: class Processor def process puts "Very important stuff here" end end module Logger def process puts "Entering process." super puts "Leaving process." end end If you just ``include Logger`` in Processor it won't work: Processor#process is looked up before Logger#process. However, if you use Module#prepend, the ancestry chain will change and calls to Process#process will be decorated as expected.