This chapter addresses the major syntactic (and partly semantic) topic of argument structure. Argument structure alternations have been central in the development of syntactic theory since Chomsky’s original transformational approach to passivization, and particularly since Fillmore’s work on ‘Case’ relations. In Pāṇinian grammar, the kāraka system provides a highly sophisticated model of argument structure, which has influenced developments in the modern Western tradition, and which also differs from modern argument structure approaches in interesting ways. The kāraka system is explained and illustrated, and compared and contrasted with modern approaches to argument alternations.