Transforming models is a critical activity in Model Driven Engineering (MDE). With the expected adoption of the OMG QVT standard for model transformation language it is anticipated that the experience in applying model transformations in various cases will increase. However, the QVT standard is just one possible approach to solving model transformation problems. In parallel with the QVT activity many research groups and companies have been working on their own model transformation approaches and languages. It is important for software developers to be able to compare and select the most suitable languages and tools for a particular problem. This paper compares the proposed QVT language and the ATLAS Transformation Language (ATL) as a step in the direction of gathering knowledge about the existing model transformation approaches. The focus is on the major language components (sublanguages and their features, execution tools, etc.) and how they are related. Both languages expose a layer...