The Chaotic Java Blog has a really nice, well-written tutorial on how to do drag and drop with GWT.

Since it might be interesting to some, this post will be about how a generic draggable component can be written. I’ve coded a draggable panel at the time to help make any Widget into a draggable version of itself, and I’ll describe how that was done.

Sure, there already exists the nice gwt-dnd library, but don’t you want to learn the basics yourself?