In the last decade Third or Additional Language Acquisition (TLA), which was previously subsumed under the field of Second Language Acquisition (SLA) or bilingualism, has started to become a subject of inquiry in its own right. One of the main areas in TLA is Cross-Linguistic-Influence, i.e. transfer, between three or more languages. This book offers an up-to-date review of the studies in this field and reports on a doctoral study carried out with adults studying L3 German with L1 English and L2 French. In order to investigate if the stage of acquisition of the third language, in this case beginners and intermediate, is a key variable in CLI, oral and written data was collected and analysed. The results indicate that the stage of L3 learning has an effect on the quantity as well as the quality of CLI in L3 productions. This book is of interest to students and scholars in the fields of second and third language acquisition and foreign language teachers who are dealing with CLI in their learners’ productions on a daily basis and are interested in research on this topic.