This paper is a reflection of our experience with the specification and subsequent execution of model transformations in the QVT Core and Relations languages. Since this technology for executing transformations written in high-level, declarative specification languages is of very recent date, we observe that there is little knowledge available on how to write such declarative model transformations. Consequently, there is a need for a body of knowledge on transformation engineering. With this paper we intend to make an initial contribution to this emerging discipline. Based on our experiences we propose a number of useful design patterns for transformation specification. In addition we provide a method for specifying such transformation patterns in QVT, such that others can add their own patterns to a catalogue and the body of knowledge can grow as experience is built up. Finally, we illustrate how these patterns can be used in the specification of complex transformations.