Broad overview of micromechanics, emphasizing the microstructure of materials, its connection to atomic structure, and its consequences on macroscopic properties. Topics include order-disorder transition; phase transformations in crystalline solids, including martensitic, ferroelectric, and diffusional phase transformations, twinning and domain patterns, active materials; kinetics of phase transformation; phase field methods with an emphasis on implementing it numerically; computationally interpret the role of diffusion kinetics and surface energy effects on nucleation and growth mechanisms; interpret the origins of material microstructures; as well as several applications to battery electrodes, ferroelectrics, and soft magnets.