  We derive a family of matrix models which encode solutions to the
Seiberg-Witten theory in 4 and 5 dimensions. Partition functions of these
matrix models are equal to the corresponding Nekrasov partition functions, and
their spectral curves are the Seiberg-Witten curves of the corresponding
theories. In consequence of the geometric engineering, the 5-dimensional case
provides a novel matrix model formulation of the topological string theory on a
wide class of non-compact toric Calabi-Yau manifolds. This approach also
unifies and generalizes other matrix models, such as the Eguchi-Yang matrix
model, matrix models for bundles over $P^1$, and Chern-Simons matrix models for
lens spaces, which arise as various limits of our general result.
