Abstract This paper is concerned with the development of auxiliary selection in Germanic, i.e. the alternation between have and be in perfects depending on the type of lexical verb. It is argued that all of the Germanic languages first develop a perfect of the modern English type, with have as the only auxiliary used with all types of verbs. This early Germanic have-perfect disallowed positional past time adverbials in the present perfect, and perfect doubling (see Larsson & Brandner to appear). In a later development, German, Dutch, and Danish developed a new perfect with auxiliary selection, a more extended use of the present perfect, and perfect doubling. It is suggested that this development is a consequence of the further grammaticalization of the auxiliary into a semantically weaker element, spelled out as either have or be (cf. Kayne 1993). The emergence of the new perfect leads to competition between two types of perfects, and to a gradual spread of the new perfect which can be observed in the historical records.