what are the hobbit movies based on?

The Hobbit is one book

There are three parts in the book.

1. Starting the journey

2. Fighting the dragon Smaug

3. Returning home

The studio decided to make The Hobbit a trilogy like they did with Lord of The Rings

And so decided to make 3 films

The Hobbit: An Unexpected Journey

The Hobbit: The Desoulation of Smaug

The Hobbit: There and Back Again

There is a book called the Hobbit. That is what it is based on. I'm sure it has additional things thrown in by the screenplay writers.

Yes. The hobbit is just one book.

The Hobbit, Lord of the rings and History of Middle Earth

The Hobbit. However, they are changed a bit from the book by the mind of Peter Jackson.

yes, the one book called "The Hobbit," but Jackson is using a lot of Middle Earth history given in The Silmarillion.

To add to TBT's remarks Peter Jackson had approval from J.R.R. Tolkien's Family

to expand on the story and gave him and the screen writers access to Tolkien's

original notes and unpublished materials.

So it all stays fairly true to Tolkiens ideas.