The study reported in the present thesis investigated the effectiveness of teaching politeness strategies, as formulated by Brown and Levinson (1987), on learners' use of these strategies in writing two types of English letters, apology and complaint letters. . An in-depth analysis of the letters written by both groups and the results of the chi-square tests revealed that the learners who received instruction on these strategies used them more frequently than those who didn't. Moreover, positive and negative politeness strategies were used by the students of both groups in writing the letters; however, in the experimental groups.