This monograph discusses the interaction of person features, case-marking, and agreement across languages, and models the variation using parameters and parameter hierarchies. In both inverse agreement and global case splits, the subject and the object determine the form of the verb or case-marking on its arguments together. After proposing a detailed, novel analysis of differential object marking in Hungarian, it is shown that similar agreement alternations and case splits in other languages can be analysed in a uniform way since they both rely on person. Languages differ in the way they grammaticalize person, however, explaining why in some languages definiteness determines agreement and case-marking, while in others animacy does. In this book, both types are analysed as interactions of hierarchically organized person features and the verb. The approach to person features adopted here captures effects of so-called person or animacy hierarchies in syntax by treating different persons as sets of features with different cardinalities, ordered by subset/superset relations. The author relates this analysis to the interaction of Case and agreement, implements existing generalizations about the alignment of case and agreement and discusses a new one: the analysis predicts exactly the attested types of case and agreement alignment in ditransitive constructions, and rules out an unattested one. The book presents data from eight different language families.