The paper addresses theoretical and practical aspects of implementing multi-stage languages using abstract syntax trees (ASTs), gensym, and reflection. We present an operational account of the correctness of this approach, and report on our experience with a bytecode compiler called MetaOCaml that is based on this strategy. Current performance measurements reveal interesting characteristics of the underlying OCaml compiler, and illustrate why this strategy can be particularly useful for implementing domain-specific languages in a typed, functional setting. © Springer-Verlag Berlin Heidelberg 2003.