What is a monad?: A monad is a design pattern concept used in mostly functional programming languages like lisp or in the modern world clojure or scala. (I would in fact copy a few things from scala.) Now why is it becoming important in java? Because java has got its new lambda feature from version 8. Lambda or closure is a functional programming feature. It allowes you to use code blocks as variables and lets you pass it around as such. I have discussed about Java's 'Project Lambda' in my previous article What's Cooking in Java 8 - Project Lambda. You can now try it out on JDK 8 preview release available in here. Now could we do monads before Java 8? Sure, after all Java's lambda is semantically just another way of implementing an interface (Its not actually that because the compiler knows where its being used), but it would be a lot messier code which would pretty much kill its utility.