This book offers an in-depth analysis of Modern English pronoun case. The author examines case trends in a wide range of syntactic constructions and concludes that case variation is confined to strong pronoun contexts. Data from a survey of 90 speakers provide new insights into the distributional differences between strong 1sg and non-1sg case forms and reveal systematic case variation within the speech of individuals as well as across speakers. The empirical findings suggest that morphological case is best treated as a PF phenomenon conditioned by semantic, syntactic, and phonological factors. In order to capture the way in which these linguistic factors interact to produce the pronoun case patterns exhibited by individual speakers, the author introduces a novel constraint-based approach to morphological case. Current case trends are also considered in a wider historical context and are related to a change in the licensing of structural arguments.