You need an API key for the application. You actually need two, a 'debug key' used for development, and when you run the app from eclipse/manual install, and the second 'signed' key you use for the released app you download from the play store. You can't use the signed one when you run from the
IDE, and you can't use the debug one when you launch from the Play store.
See:
https://developers.google.com/maps/documentation/android/start
Which describes getting each type of key, and how to use them.