A hierarchy of equations for the distribution function in statistical mechanics. This hierarchy leads to kinetic equations that are generalizations of the Boltzmann equation and it has given important insights into the approach to equilibrium in statistical mechanics. The initials BBGKY stand for N. N. Bogoliubov, Max Born, H. S. Green, J. G. Kirkwood, and J. Yvon, who derived this hierarchy of equations in the 1930s and 1940s.