  Micrometre sized colloidal particles can be viewed as large atoms with
tailorable size, shape and interactions. These building blocks can assemble
into extremely rich structures and phases, in which the thermal motions of
particles can be directly imaged and tracked using optical microscopy. Hence,
colloidal particles are excellent model systems for studying phase transitions,
especially for poorly understood kinetic and nonequilibrium microscale
processes. Advances in colloid fabrication, assembly and computer simulations
have opened up numerous possibilities for such research. In this Review, we
describe recent progress in the study of colloidal crystals composed of tunable
isotropic spheres, anisotropic particles and active particles. We focus on
advances in crystallization, melting and solid solid transitions, and highlight
challenges and future perspectives in phase transition studies within colloidal
crystals.
