  We present a geometric proof of the Poincar\'e-Dulac Normalization Theorem
for analytic vector fields with singularities of Poincar\'e type. Our approach
allows us to relate the size of the convergence domain of the linearizing
transformation to the geometry of the complex foliation associated to the
vector field.
  A similar construction is considered in the case of linearization of maps in
a neighborhood of a hyperbolic fixed point.
