Teaching Essay Writing Through Inquiry Based Learning to ESL Learners The present research investigates the effectiveness of using Inquiry Based Learning in teaching essay writing skills to ESL learners. 40 ESL learners were selected from two sections from International Islamic University Female Campus Islamabad, Pakistan and divided into two groups; control and experimental. The control group was taught essay writing skill through the traditional method; while the experimental group was taught through Inquiry Based Approach. The lesson plans were developed according to 5E Inquiry Based Model and administered to the experimental group. This research is quantitative and experimental in nature and as such follows a comparison between control and experimental groups using pre and post-tests. The other secondary research instruments are questionnaire based on five point likert scale and the reflective comments of the students to get feedback of experimental group at the end of the study. Pre and post-tests and questionnaires were analyzed quantitatively using SPSS. However, students' reflective comments were analyzed qualitatively through content analysis. Results and interpretations of data proved the hypothesis and confirmed that Inquiry Based Approach is helpful in improving essay writing skills of ESL learners. This (approach was found more effective than traditional method of teaching writing skills as it enhanced learners' critical thinking skills and autonomy). On the basis of the findings some suggestions are presented to English language teachers of Pakistan to solve the problems of ESL learners of Pakistan in essay writing.