Molecular science entails the study of structures and properties of materials at the level of single molecules or small interacting complexes of molecules. Moving beyond single molecules and well‐defined complexes, aggregates (i.e., irregular clusters of many molecules) serve as a particularly useful form of materials that often display modified or wholly new properties compared to their molecular components. Some unique structures and phenomena such as polymorphic aggregates, aggregation‐induced symmetry breaking, and cluster excitons are only identified in aggregates, as a few examples of their exotic features. Here, by virtue of the flourishing research on aggregation‐induced emission, the concept of “aggregate science” is put forward to fill the gaps between molecules and aggregates. Structures and properties on the aggregate scale are also systematically summarized. The structure–property relationships established for aggregates are expected to contribute to new materials and technological development. Ultimately, aggregate science may become an interdisciplinary research field and serves as a general platform for academic research.

Restriction of intramolecular motion (RIM) is the widely-accpeted mechanism of aggregation-induced emission (AIE). In this concise and comprehensive perspective, four mechanistic models related to different nonradiative pathways are summarized with examples to disclose the connotation of RIM, and meaningful mechanistic topics for future researches are advised.