In the two decades since the discovery of AIE, research in this field has grown exponentially, with over 2000 AIEgens being recorded in the universal database for aggregate science. As the focus shifts from investigating individual AIE to exploring aggregate science, controlling the molecular aggregation process has emerged as a key challenge. In addition to synthesizing new AIEgens, understanding and regulating molecular aggregation has emerged as a pivotal objective on the path to understanding the "aggregate science." Controllable molecular aggregation bridges the gap between solutions and solids. Broadly, it enables polymorph control, an aim pursued throughout physical chemistry but achieved thus far mainly by trial and error. Most reported polymorphs differ only in molecular packing. Conformational polymorphs are rarer and more challenging to control, as molecules must overcome energy barriers to adopt different conformations in the solid state. Conformational AIEgen polymorphs are especially interesting, as different conformers can possess distinct electronic properties, essentially behaving as different molecules.