The generic programming paradigm has exerted great influence on the recent development of C++, e.g., large parts of its standard library [2] are based on generic containers and algorithms. While templates, the language feature of C++ that supports generic programming, have become widely used and well understood in the last years, one aspect of templates has been mostly ignored: template template parameters ([2], 14.1). In the first part, this article will present an in depth introduction of the new technique. The second part introduces a class for arbitrary precision arithmetic, whose design is based on template template parameters. Finally, we end with a discussion of the benefits and drawbacks of this new programming technique and how it applies to generic languages other than C++.