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Answer : MVP exists to tackle God Activity problem (An Activity/Fragment that has way too many lines). While it wasn't obligatory (you can code in any pattern that you want), many developers agree that MVP is suitable for Android. It makes your source code cleaner, testable, maintainable and robust. You can think of an interactor as your "Model/Controller". An interactor will fetch data from your database, web services, or any other data source. After getting the data, the interactor will send the data to the presenter. Thus, making changes in your UI. Advantages of using interactor in a separate class is that it will decouple your class, thus making it cleaner and testable. Sure, you can put the interactor in your presenter inner class, but what's the point? The disadvantages of putting the interactor in your presenter is it will make your presenter class bigger and relatively harder to read and manage. Update: Of course this is just an over-simplification...

Answer : Fist of all: I believe that you are mixing up the MVC pattern and n-tier-based design principles. Using an MVC approach does not mean that you shouldn't layer your application. It might help if you see MVC more like an extension of the presentation layer. If you put non-presentation code inside the MVC pattern you might very soon end up in a complicated design. Therefore I would suggest that you put your business logic into a separate business layer. Just have a look at this: Wikipedia article about multitier architecture It says: Today, MVC and similar model-view-presenter (MVP) are Separation of Concerns design patterns that apply exclusively to the presentation layer of a larger system. Anyway ... when talking about an enterprise web application the calls from the UI to the business logic layer should be placed inside the (presentation) controller. That is because the controller actually handles the calls to a specific resource, queries the data by...