"Restitution" means the law of unjust enrichment. As a basis of liability, it is as fundamental as contract or tort. "You are liable to me, not because you promised to do anything, and not because you necessarily caused me any injury, but because (if the law did nothing) you would be unjustly enriched at my expense." Claims on this basis arise across the whole range of private law. This gives restitution as much variety as any other subject and makes it an essential part—frequently overlooked—of the analysis of many legal problems.
Course materials will consist of a new casebook (not yet published) being produced by Dean Farnsworth and Professor Kull. Anyone who is curious is welcome to come by Professor Kull's office and have a look.