This article offers a proposal for integrating the social network Facebook into an English as a Foreign Language (EFL) classroom in tertiary education. The main objectives of this article are the following: (1) to offer a pedagogical proposal so that students can develop written skills and grammar at the same time that they acquire social competences using Facebook; and (2) to know students' opinions about the use of Facebook and the main social competences that they have acquired while using this social network in the teaching-learning process. The methodology is mainly qualitative-descriptive although some quantitative data is offered with the results of a questionnaire students completed. The data were collected through students' posts in the Facebook discussions and a questionnaire. The findings reveal the main grammar mistakes observed in students in the Facebook discussions and how Facebook is an appropriate social network for the participation of students in cooperative discussions on social topics and for the acquisition of social competences such as cooperation or communication. The results of the questionnaire show that students have a positive opinion about practicing the written skill in Facebook and they are aware that, apart from learning English, they also acquire social competences.