First Language versus Foreign Language deals with the «battle» that takes place in writers' heads when writing in a foreign language. Most academics today need to write in another language than in their first language (L1) in order to publish in internationally recognized journals. However, as writing research has shown, writing in a foreign language (FL) presents difficulties. The study compares L1 and FL writing, analysing written texts and the writing processes in terms of fluency, errors and revision. It takes a closer look at the «battle» between the L1 and the FL and offers useful insight. The findings allow a glimpse at the processes that take place in the brain, calling for new didactic approaches to FL writing.