peteOCAELN.engin.UMich.EDU We have developed a new style of semantic definition called high-level semantics. In constrast to traditional de-notational semantics, high-level semantics is suitable for both defining the functional meaning of programming lan-guages, as well as describing realistic compiler implcmen-tations. Moreover, high-level specifications are consid-erably more descriptive and intelligible than traditional specifications. This paper describer the compiler generator MESS, which embodies the principles of high-level semantics. MESS has been used to generate compilers for nontrivial languages. The compilers are efficient, and produce ob-ject programs that are competitive with those generated by hand-written compilers. 1