In many areas of education, commerce, and public policy, there is a need to understand the functional language abilities of individuals in bilingual populations. The current project aims to produce an easy-to-use instrument that can quantify language use patterns, language proficiency, and language dominance in the two languages of bilinguals. These dimensions will be measurable in absolute terms (as scores) and in relative terms (as proportional scores in the two languages). The instrument can be administered by a non-specialist, and will take 7-10 minutes to complete. By virtue of its modular design, it can be adapted to specific needs by selection of appropriate subtests. A guide to interpretation of results will enable teachers, administrators, policy makers, and researchers to understand the language-functional profiles of individuals and groups of testees. The project goals include development of the instrument in Spanish, French, Catalan, and English versions.