The Wulff construction is a method to determine the equilibrium shape of a droplet or crystal of fixed volume inside a separate phase (usually its saturated solution or vapor). Energy minimization arguments are used to show that certain crystal planes are preferred over others, giving the crystal its shape. It is of fundamental importance in a number of areas ranging from the shape of nanoparticles and precipitates to nucleation. It also has more applied relevance in areas such as the shapes of active particles in heterogeneous catalysis.