This book deals with the category of case and where to place it in grammar, in particular how the morphological expression of grammatical function should relate to formal syntax. In the generative tradition, this issue was dealt by the influential proposal of the dissociation between abstract syntactic Case on the one hand, as a means for nominals to be licensed in the derivation, and the morphological expression of case on the other, as an idiosyncratic property of individual languages that is not always necessarily present. However, the expansion of the empirical picture in terms of cross-linguistic variation has brought theoretical tension and it becomes increasingly clear that the mapping of morphology and syntax is not ‘one-to-one’. Our book deals with a number of key issues on this ongoing debate that map onto, roughly, its three parts. The first one has to do with the modes that we need for structural case assignment: whether we only need one or two and whether these are Agree-based (where Case is a reflex of agreement) or dependent case based (where Case is assigned configurationally to nominals in a certain domain). This part also discusses how Case would relate to a theory of parameters. The second theme and part of the book deals with what traditionally has been labelled as the division of labour between structural and inherent case, synchronically but also diachronically. And finally, the third part of the book deals with individual cases and how they can illuminate case theory.