This dissertation investigates the overlap of morphological case marking and event structure in Russian and Lithuanian, as well as highlighting issues in the traditional distinctions of structural and non-structural case. I follow Babby (1994) in distinguishing between two kinds of non-structural cases. Lexical case is licensed by particular lexical items, and is unpredictable on the basis of thematic role or semantic function. Semantic case is both linked to thematic role and semantic interpretation. I adopt an event structural analysis of argument structure, following Ramchand 2008's framework. She proposes that argument structure relations are represented in the syntax, in an expanded vP which is composed of functional heads that correspond to the subevents denoted by a predicate: initiation, process and result. Thus, argument structure is based on the structural relationships of arguments and these subevents. I examine two specific instances of non-canonical case marking in Lithuanian and Russian, with the goal of accounting for the case marking facts through an event structural analysis. The first is the phenomenon of oblique passivization. Contrary to claims in the literature (Freidin 1992, Woolford 2006), both Russian and Lithuanian allow passivization by verbs that require a case other than accusative on the internal argument. However, passive participles from oblique case verbs do differ significantly from those formed from accusative case verbs: the former do not allow for the statal, adjectival function of the passive. I argue that this is due to the fact that verbs that license oblique case on their internal arguments are always atelic (following Richardson 2007), which entails the absence of a result state. This results in a difference in syntactic structure between accusative and non-accusative case marking verbs, and accounts for the differences in the functions of passive participles. The second case marking phenomenon is accusative-instrumental case alternations, allowed by certain semantic classes of verbs in Russian and Lithuanian. In this alternation, the accusative is regularly used to indicate that the internal argument rates highly on the Proto Patient scale (in the sense of Dowty 1991). The instrumental case is used to indicate that the internal argument is interpreted as a means. I propose an event structural analysis of these alternations, arguing that the accusative is used when the internal argument occupies the structural position of an undergoer, highlighting that this argument is undergoing some change of location or state during the action described by the verb. Instrumental arguments are paths, arguments that modify the predicate, but do not undergo change themselves. These two phenomena also provide evidence for a structural difference between lexical and semantic case. Under my analysis, lexical case can be licensed in the same position as structural case, while semantic case cannot.