It was conjectured in the early 1950’s that the empirical
spectral distribution of an $n \times n$ matrix, of iid entries, normalized by
a factor of $\frac{1}{\sqrt{n}}$, converges to the uniform distribution over
the unit disc on the complex plane, which is called the circular law. Only a
special case of the conjecture, where the entries of the matrix are standard
complex Gaussian, is known. In this paper, this conjecture is proved under the
existence of the sixth moment and some smoothness conditions. Some extensions
and discussions are also presented.