This dissertation presents a discussion of argument realization on the basis of theta-roles and case. Parametric variation between languages like Greek, on the one hand, and languages like Italian and French, on the other, is captured by a theory of lexico-syntactic operations on theta and case features very much based on Reinhart''s Theta System. The comparison of Greek and Italian/French reveals that Greek lacks reflexivization and reciprocal formation of benefactors, as well as certain types of impersonals. This follows from one generalization: only the argument that would otherwise appear in the accusative case may be reduced in all instances of argument alternations in Greek. This thesis is of interest to researchers concerned with argument structure realization, and the way lexical information affects the syntactic derivation, and to scholars working on Greek and on Generative Syntax more in general.