Clitics are a challenge for any view of the architecture of grammar because they straddle the boundaries between words and morphemes and between syntax and morphology. The paper shows that clitics are syntactic words which also serve as word-parts, so their presence is explained in terms of syntactic dependencies, but their position follows morphological rules. The general analytical framework which is proposed builds on the theory of Word Grammar. As expected, clitics do demand a collection of special analytical categories - the word-classes Clitic and Hostword, and the relationships 'host', 'clitic', 'finite verb' and 'extension' - but (unlike other current theories of cliticization) they do not need any extra theoretical apparatus. The paper considers simple clitics in English and special clitics in French and Serbo-Croat.