By looking beyond their written products into what they do as they write, this mixed methods study offers insights into the writing process of writers who have mastered one language and those who have mastered two. It investigates the cognitive effects of bilingualism and biliteracy on the writing processes of years ten and eleven Sydney high school writers across three groups (N = 30): English monolinguals, Chinese-English bilinguals, and Chinese-English biliterates, focusing on their formulation processes (i.e., how thoughts are converted into language and the written form). Findings indicate distinctive features and patterns of writing behaviours, possibly reflecting specific strengths and weaknesses for each group. The monolinguals demonstrated strategic use of vocabulary, while the biliterates and bilinguals demonstrated prospective and retrospective behaviours when formulating. These findings are discussed in light of studies on the writing process and on the effects of bilingualism.