Abstract
 Irene Heim’s 1983 paper, “On the Projection Problem for Presuppositions” is, first, a paper about presupposition projection. But perhaps its major significance lies in its role in launching the dynamic turn in formal semantics, whose central idea is that the conventional meaning of an expression is given by a description of how that expression updates a context. The fundamental ideas of context and context change that Heim presented in this brief paper are now part of the basic toolkit of semantics. At the same time, the paper established presupposition and presupposition projection as a topic of central concern for the emerging dynamic approach. In this commentary, I briefly describe the paper’s most direct antecedents, review its central theoretical innovations, and describe some alternative approaches to the formal characterization of contexts and to the analysis of presupposition and presupposition projection.