  Several mechanisms of bar formation in stellar galactic disks are considered,
including Toomre swing amplification and normal mode approach. On example of
the well-known model of Kuzmin--Toomre using N-body simulations it was shown
that the stellar bar is developed as a result of the evolution of an unstable
normal mode. The pattern speed and the growth rate found agree well with linear
perturbation theory. Nonlinear evolution of the bar is followed. Role of the
growing transient spirals in bar formation is discussed.
