All Basque dialects have four distinct morphemes which can be affixed to the finite verb form, the choice between which depends on the internal structure of the embedded clause and its type of insertion in the matrix clause. 1 The paper is organised as follows. Section 2 introduces the four complementiser-like affixes and illustrates some of their main uses. Section 3 provides direct evidence drawn from embedded interrogatives for the necessity of postulating several layers in the left-peripheral or CP domain. Finally, in section 4, examples will be discussed which show that in some contexts, the otherwise well-established distinction between '[Semi] free relatives' and embedded wh- "semi-questions" (which both translate sentences like ...what they've done) is apparently neutralised, although some semantic and pragmatic differences subsist.