Clitic climbing, the phenomenon where a clitic pronoun selected by a complement verb attaches to a host verb, is found in a number of languages. In this chapter its properties (such as the types of host verbs, the temporal properties of the infinitival domain, and the degree of adjacency between host and complement verb) and interactions with a series of “transparency effects” (such as Long DP Movement, Long Null Operator Movement, and Auxiliary Shift) are critically reviewed in various Romance languages. From there the chapter explains the traditional account for clitic climbing in a transformational framework, where it was seen as the output of two rules: Restructuring and Clitic placement. It then explores different lines of approaches for its derivation, in the Government and Binding framework and in the Minimalist Program. These crucially involve assuming one of these operations or structures: head movement; VP movement to the edge of the complement domain; the optional status of the host verb, as an auxiliary verb or as a lexical verb; the consistent auxiliary status of the host verb. From there, the implications of some these analyses for cross-linguistic and intralinguistic variation are discussed. The chapter concludes with: a summary of the main characteristics of clitic climbing and a list of topics for further research.