This document describes the Conceptual Learning and Development (CLD) model of concept formation. According to the CLD analysis, a single concept is learned in the following successive levels of attainment: concrete, identity, classification, and formal. The four levels are considered applicable to concepts that are defined (or could be defined) in terms of attributes and have actual perceptible examples. CLD breaks down the ways in which concepts can be extended and used at each level, as well as the operations involved in concept learning at each level. Acquisition and remembering of names of concepts may come at any one of the levels and is only essential for formal conceptualization. This overview focuses on developmental aspects of the model, particularly certain predictions which will be empirically tested. These involve; (1) age influences on level of attainment and ways in which concepts are used, (2) individual differences, (3) invariant sequences through all applicable concepts, and (4) relationships between having labels for the concept and attainment of levels as well as mastery of its uses. The conditions of learning for each level are categorized into internal (discussed in terms of operations and attainment at the preceding level) and external (concerned with task and instructional variables that facilitate learning) factors. Finally, a discussion of relationships between CLD and other viewpoints is included. (DP)