Much of the English text on the web is written by people whose native language is not English. Many English as a Second Language (ESL) writers, even those with a high level of proficiency, make common grammatical mistakes. In this talk, I will present some of our recent work on modeling ESL writings. I will first talk about characterizing ESL students’ writing revision process with syntax-driven machine translation models. Then, I will focus on modeling similarities in ESL writers’ preposition selection mistakes using a distance metric learning algorithm.