  The purpose of this paper is to study finite-dimensional Lie algebras over a
field k of characteristic zero which admit a commutative polarization (CP).
Among the many results and examples, it is shown that, if k is algebraically
closed, the nilradical N of a parabolic subalgebra in A_n and C_n has such a
CP. Using this fact a simple closed formula is derived for the index of N.
