A discussion of what functional linguistic research can offer teachers of composition and English is presented in this paper, which provides examples of different levels of analysis (phonology, morphology, and syntax) for the language of a variety of populations (including traditional freshmen, basic writers, English as a second language (ESL) students, and nontraditional, re-entering adult students). The paper presents the aims and theoretical orientation of functional linguistics, discusses how functional linguistics can provide insight into the processes used by ESL students acquiring English phonology, and shows how functional analysis can be used to correct the problem of overusing and misusing nonrestrictive relative clauses. It then shows how functional analysis can inform advanced and adult composition students of the uses and value of various stylistic language patterns, using the functions of the passive voice as an example, and recommends increasing students' awareness of derivational morphology and its role in word formation in English. (EL)