Measurement in learning and instruction is discussed here in the light of instructional design requirements and specific models or systems of instruction. Three general classes of instructional models found in current educational practice are presented. One particular model of instruction--for adapting instruction to individual differences--is described, and its testing and measurement implications are discussed. The description of the instructional model is followed by considerations of (a) the analysis of performance domains, (b) individual assignment to instructional alternatives, and (c) measuring what is learned by means of criterion-referenced tests. These topics are discussed in terms of the measurements required to make instructional decisions about individual learners. In the last section, the topic of evaluating and improving an instructional system and its components is discussed. A list of references, tables, and illustrations are appended. (Author/JY)