This study will address the so-called “auxiliary puzzle”, trying to find an answer to the following questions: (i) what is the status and function of auxiliaries or auxiliary verbs? (ii) what can they tell us about the structure of language in general? (iii) are they verbs or functional elements? (iv) are they verbal elements inserted in the functional domain of a clause? (v) are they inserted inside or outside the VP constituent? (vi) is the position which they occupy relevant in any way? (vii) are auxiliary configurations mono- or biclausaP (viii) do auxiliaries occupy the same structural position in a language or across languages? (ix) can we provide a crosslinguistic definition of auxiliaries?