We give some relations between Jacobians and minimal polynomials of n
polynomials in n variables, which yield some new effective criteria to
decide whether a polynomial or a rational map is invertible, and to c
alculate the inverse if it exists. Our new criteria work for all ratio
nal maps from K-n to K-n, where K is an arbitrary field. We also formu
late a conjecture, which is equivalent to the Jacobian conjecture.