Modeling Ungrammaticality in Optimality Theory presents a collection of papers in phonology and syntax on the topic of ineffability, or absolute ungrammaticality. The papers all contribute new analyses of carefully presented cases, making the book useful for researchers exploring ineffability from any theoretical perspective. The theoretical context for the papers is the analytical challenge which these cases present for Optimality Theory. The architecture of OT takes an input and maps it onto its optimal output. But the cases analyzed in these papers would seem to invite analyses in which an input has no output whatsoever, not even an imperfect one. The papers develop various strategies for modeling this phenomenon, building on proposals in the literature such as the null parse, control theory, the null output, optimal gaps, string-based correspondence theory, and others.