Some applications will require a writing sample.

This is usually a short piece of written work, approximately 10-15 pages, that demonstrates to the admissions committee your ability to put together clear arguments that are supported by well-researched theory and findings. Ideally, your writing sample submission should be on a topic related to your proposed research interests. If you were fortunate enough to work with a professor on a paper, then seek permission from the professor to use that work as a writing sample.

Alternatively, you can use the best research paper from a course. If you do, make sure the paper is reviewed by peers and professors before submission. Just as with the statement of purpose, your writing sample must be perfect.