My interviewer (who says he has a Ruby and Java background) was claiming that Ruby modules are interfaces (like in Java) and seemed annoyed that I didn't agree. I told him that Ruby modules are ways of grouping methods to be shared between classes whereas Java interfaces are specifications of class behavior . Furthermore, because Java is statically typed, interfaces can be used in method signatures. But because Ruby is dynamically typed, you don't need to specify the type of a method's arguments. Another reason why Ruby modules aren't like Java interfaces. My interviewer seemed annoyed that I brought these points up. Perhaps he meant that modules are the interfaces of Ruby in a more general or abstract sense, but if so, he should have elaborated more on why. Instead, he was just dead silent after I made my points. If he's a reflection of LinkedIn's engineering culture, then I say it was a bullet dodged.