  The concept of perturbative gauge invariance formulated exclusively by means
of asymptotic fields is used to construct massive gauge theories. We consider
the interactions of $r$ massive and $s$ massless gauge fields together with
$(r+s)$ fermionic ghost and anti-ghost fields. First order gauge invariance
requires the introduction of unphysical scalars (Goldstone bosons) and fixes
their trilinear couplings. At second order additional physical scalars (Higgs
fields) are necessary, their coupling is further restricted at third order. In
case of one physical scalar all couplings are determined by gauge invariance,
including the Higgs potential. For three massive and one massless gauge field
the $SU(2)\times U(1)$ electroweak theory comes out as the unique solution.
