The engineering of particles with customized properties optimized for dosage form manufacture (tablet, capsule, ointment, etc.) has long been a goal of the pharmaceutical industry. Particles can be designed through modification in the size, morphology, and packing arrangement of the solids. The most common approach in achieving this is through crystallization. In this bottom-up process, the two main steps, nucleation and crystal growth, both play a decisive role in shaping the quality of the final crystalline product. In this review, the role of nucleation and crystal growth in controlling particle properties is discussed, and examples are provided that demonstrate the variation in solid-state properties as a function of size, habit (morphology), and internal structure of the particles. In addition, the role of particle properties in product performance and dosage form development of pharmaceuticals is also discussed.