An examination of measures currently used to assess degree of bilingualism in individuals looks at the problems inherent in them, ideal measures, and how to use available measures. It is suggested that definition of bilinguality is a central cause for measurement problems, since a bilingual is assumed to be the sum of two monolinguals, without regard to the specific competence of a bilingual; reconceptualization of bilinguality is recommended. Analysis then looks at two types of measurement, formal and informal. Formal measurement is divided into traditional (focusing on grammar, pronunciation, and vocabulary) and behavioral (language balance and dominance) measures. Problems with traditional measures include lack of measures for native speakers, loss of test validity through translation into another language, examiner unfamiliarity with the language or culture, and minimal measurement of communicative competence. Behavioral measures, which assume that language tasks would elicit similar performance in both languages, have questionable validity. Informal measurements include language background questionnaires and ethnographic data collection. Both are found to have methodological limitations, principally lack of precision and possible researcher bias. It is recommended that researchers use a combination of currently available measures, depending on the kind of information needed. Contains 17 references. (MSE)