A discussion of the relationship of second language course content and testing focuses on the instruction and assessment of language proficiency. Basic principles of measurement of proficiency and syllabus design for proficiency and their implications are examined. An approach is recommended to syllabus design that has the learner's real needs at its center, sets realistic goals in light of those needs, and identifies language content that will both satisfy those needs and lead to the desired proficiency levels. It is concluded that proficiency rating scales provide the most valid and reliable means of measuring practical proficiency and also contribute to the process of course design. (MSE)