This article presents a case study which aims at analyzing the influence that the first language has on the learning of a foreign language. This research was conducted in an ESL classroom from a Language Center in England and was carried out with a Saudi Arabian student during a two-month period. In order to conduct this research, theoretical support about contrastive analysis (CA) and error analysis (EA) were taken into account. The findings of this case study suggested that CA and EA are effective ways to study and understand how the first language (L1) of a learner might have an influence on the learning process in a foreign language. In this particular case study, it was found that this Saudi Arabian learner had a better performance in receptive skills; there were some evidences of U shape learning in this learner and also it was noticed that his handwriting and the use of punctuation marks although good, they needed some improvement.