Peter D. Mosses is known for his many contributions in the area of formal program semantics. In particular he developed action semantics, a combination of denotational, operational and algebraic semantics.

The presentations - given on a symposium in his honor in Udine, Italy, on September 10, 2009 - were on subjects related to Peter's many technical contributions and they were a tribute to his lasting impact on the field. Topics addressed by the papers are action semantics, security policy design, colored petri nets, order-sorted parameterization and induction, object-oriented action semantics, structural operational semantics, model transformations, the scheme programming language, type checking, action algebras, and denotational semantics.