  The critical temperature of Bose-Einstein condensation essentially depends on
internal properties of the system as well as on the geometry of a trapping
potential. The peculiarities of defining the phase transition temperature of
Bose-Einstein condensation for different systems are reviewed, including
homogenous Bose gas, trapped Bose atoms, and bosons in optical lattices. The
method of self-similar approximants, convenient for calculating critical
temperature, is briefly delineated.
