'Introduction to Programming with Greenfoot' is the official book used by both teachers and students.
The second edition of the book is out now.
The new edition has several new chapters; new scenarios; end-of-chapter drill and practice sections added; more gradual introduction; improvement of presentaion of key concepts; new Greefoot features included; programming with Microsoft Kinect.
Please visit the book's web page for more information about this new edition.
Learn how to use Greenfoot and begin programming:
See the how-to board for guides on commonly asked questions about how to accomplish various things in a Greenfoot scenario.
The Greenfoot API is available online. You can also access it from within Greenfoot - use the "Greenfoot Class Documentation" menu item, from the Help menu.
German translations are available for some videos (thanks to Frajo Ligmann).
There are many more things you can do with Greenfoot, such as:
The Greenfoot FAQ list covers many frequently-asked questions.