Jacobian algebras are obtained from the Weyl algebras by inverting certain elements (not in the Ore sense). Surprisingly, these algebras have little in common with the Weyl algebras: in fact, they have almost opposite properties. The Jacobian algebras appeared in my study of polynomial automorphisms and the Jacobian Conjecture, which is a conjecture that makes sense only for polynomial algebras in the class of all commutative algebras (it is a theorem). In order to solve the Jacobian Conjecture, it is reasonable to believe that one should develop techniques which make sense only for polynomials. The Jacobian algebras are a step in this direction (they exist only for polynomials and make no sense even for Laurent polynomials).