The paper by Natascha Müller follows the new way of studying bilingual first language acquisition which has been advocated in the last few years by several researchers (Döpke, 1996, 1997; Gawlitzek-Maiwald & Tracy, 1996; Hulk & Van der Linden, 1996; Hulk, 1997). In this new approach, while it is taken as an established fact that bilingual children are capable of early language differentiation, at the same time a lot of attention is given to cross-linguistic influence as an important characteristic of bilingual first language acquisition. We will discuss the nature of differentiation and transfer here as presented by Müller's paper and the way we see it ourselves. We will illustrate our position with examples from the French-Dutch bilingual child we have been studying for some time.