This handbook, which focuses on foreign language teaching in the classroom, aims to describe the "state of the art" in testing. The first section considers the area of aptitude testing, particularly the diagnostic function of aptitude tests. A taxonomy of foreign language teaching objectives points out the need to classify the aims of foreign language instruction. Another section on measuring achievement explores techniques and recent research, strongly urging the use of criterion-reference tests. The use of tests in the classroom and methods of evaluating teacher competence are discussed. Research needs are spelled out and a bibliography offered. Several tables graphically illustrate key concepts in this paper. (RL)