I would like to thank my supervisor, Dr. Hoshang Farooq Jawad, who is Associate Professor of Linguistics in Sulaimani University, for the patient guidance, encouragement and advice he has provided for me. This work is concerned with the register-related errors of 4th grade students' writings in English departments of Salahaddin University. Students are expected to be formal in their written responses, since they study in an academic environment such as university. They are expected to write in a way which suits the university language level. The present work aims at identifying errors committed by the students in using English words without any regard to the types of register they belong to, finding out the reasons why these indiscriminate uses of register are committed by the students, and finding out which type is used more frequently in comparison to others. Chapter one: Introduction Chapter two: Theoretical Background Chapter three: Date Collection Chapter four: Data AnalysisChapter Five: Conclusions