We present this study on writing skill in the field of teaching Arabic to nonnative speakers. This study comes as a continuation of two previous studies that we presented on language skills in general and the skills of listening and reading in particular. In the future, we want to pursue research on linguistic skills in applied linguistics . Our focus on studying linguistic skills in applied linguistics comes from our belief in the benefit that results from these studies to facilitate the teaching of Arabic to non-native speakers, and to meet an urgent need to find the easiest ways to teach the increasing number of those wishing to learn Arabic We began the study with a definition of the skill and its components, then moved on to talking about and defining language skills. After that, we talked about the skill of writing, so we defined it and defined its components, then shed light on the relationship of writing skill with other language skills. We also talked about the aspects that a teacher should focus on when training his students in the classroom. Then we made an extensive presentation of the most important abilities that fall under the skill of writing at the language levels (beginner - intermediate - advanced). After we demonstrate these capabilities, we choose what we deem appropriate. After we finished talking about writing skill, we moved on to talk about how to test the writing skill of a foreign Arabic language student. We presented the aspects that will be tested, and the types of questions that will enable us to be tested .