Some US researchers and practitioners are calling for the use of written codeswitching in mainstream college courses, despite a strong English-only sentiment among many teachers and the public. This paper describes the existing positions in this debate and presents findings from the author's research to shed light on the debate and make recommendations for the classroom. The research describes the functions of codeswitching found in 47 personal letters exchanged between two young adults. Findings indicate that there are many similarities between the functions of informal written and oral codeswitching. Also, not all bilinguals codeswitch or do so with the same frequency. In addition, bilinguals who codeswitch in writing are more likely to do so in informal situations among other codeswitching bilinguals than in formal school environments. Written codeswitching provides an unsurpassed opportunity for bilingual students to fully express themselves, but its use in the classroom runs counter to linguistic and cultural norms and must be guided by an informed and sensitive instructor in an appropriate context.