Hyperkähler manifolds are higher-dimensional generalizations of K3 surfaces. The Beauville conjecture predicts that the number of deformation types of compact irreducible hyperkähler manifolds is finite in any dimension. In this talk I will briefly discuss some basic notions of the theory, explain why hyperkähler manifolds play a very important role in classification of complex manifolds, and then explain what are the evidences for Beauville's conjecture.