Manipulation during aggregation is to control the structure of molecular precipitation from solutions by adding poor solvents and evaporating solvents. Both thermodynamic and kinetic factors control this process and can be regarded as controllable polymorphism, , which is of great challenge. The precipitation of molecules can be either amorphous or crystalline, depending on the practical implications. The approaches of controllable polymorphism include (i) transformation from the amorphous to crystals and (ii) induction of crystals with multiple phases.