This book reports the results of an extensive study of slips of the tongue produced by foreign language (L2) learners at different levels of proficiency. Thus, it provides new data which can be used to test current monolingual models of speech production and to further the development of bilingual speech production models. Moreover, it offers a new approach to the study of second language acquisition. The book contains a detailed survey of the findings of L1 slip research, including studies of slips produced by child L1 learners. It systematically compares these findings to those of the current L2 study and relates them to recent monolingual and bilingual models of speech production and to several cognitive models of second language acquisition. Special features of the book are its emphasis on methodological problems and the inclusion of the complete L2 corpus of 2000 slips of the tongue.