Declarative concepts (i.e., key terms with short definitions of the abstract concepts denoted by those terms) are a common kind of information that students are expected to learn in many domains. A common pedagogical approach for supporting learning of declarative concepts involves presenting students with concrete examples that illustrate how the abstract concepts can be instantiated in real-world situations. However, minimal prior research has examined whether illustrative examples actually enhance declarative concept learning, and the available outcomes provide weak evidence at best. In the three experiments reported here, students studied definitions of declarative concepts followed either by illustrative examples of those concepts or by additional study of the definitions. On a subsequent classification test in which learners were presented with examples and were asked to identify which concept the example illustrated, performance was greater for students who had studied illustrative examples during learning than for students who only studied definitions ("d"s from 0.74 to 1.67). However, the effects of illustrative examples on declarative concept learning depended in part on the conditions under which those examples were presented. Although performance was similar when examples were presented after versus before concept definitions (Experiments 1a-1b), classification accuracy depended on the extent to which examples of different concepts were interleaved and whether definitions were presented along with the examples (Experiment 2).