This book provides an in-depth investigation of single and double cliticization based on research in theoretical syntax and first language acquisition. Although the main focus is the analysis of data from Bulgarian, the work draws crosslinguistic parallels to some of the Romance and Balkan Sprachbund languages. Acquisition data from three original experimental studies with 79 typically-developing monolingual Bulgarian children aged between 2 and 4 are reported. This is the first study of the placement properties of object clitics in both pre- and post-verbal positions, and of the acquisition of clitic doubling for Bulgarian. The reported research has direct relevance to the current debate of the crosslinguistic variance in the acquisition of clitics.