Platinum has been widely used in many applications, especially for catalysis and fuel cell technology due to its ability to maneuver both oxidation and reduction reactions. In addition to size, the shape or morphology of a Pt nanocrystal provides a sensitive knob for tuning its catalytic and electrocatalytic properties. A number of chemical routes have been developed to produce Pt nanocrystals with well-defined and controllable shapes to improve their performance in terms of catalytic activity and selectivity. Conventional polyhedrons (e.g., cubes, octahedrons, and tetrahedrons) and their overgrown structures (e.g., multipods) have all been obtained in reasonably high yields, as well as some unconventional shapes (e.g., tetrahexahedrons). Compared to commercially available Pt catalysts, these well-defined nanocrystals exhibit greatly enhanced activity and selectivity for a range of reactions.