My postdoctoral project aims to examine the effect of two types of instruction - explicit vs. implicit instruction - on the acquisition of the German case rules by Dutch-speaking second language learners. The general research question is: which type of instruction is more effective? In addition, the effectiveness of the different types of instruction will be related to the interplay between knowledge and use of the German case rules. This interplay refers to the situation where learners can obtain the explicit knowledge about the case rules (‘knowing’), but fail to gain the implicit knowledge needed to freely use these rules in spontaneous speech (‘using’). In examining the effect of instruction on the explicit and implicit knowledge of the German case rules, a distinction will be made between simple and complex rules. The question is then: which rules, either simple or complex, benefit more from which type of instruction (explicit or implicit)? To investigate the effectiveness of both types of instruction on knowledge and use of German case rules, I will gather empirical data from different groups of advanced learners of L2 German, whose performance regarding both simple and complex case rules will be examined quantitatively through statistical analysis as well as qualitatively through the interlanguage analysis of individual learners.