  We consider generalizations of the standard model (SM) which are based on the
gauge symmetry $SU(n)_c\otimes SU(m)_L\otimes U(1)_N$. Although the most
interesting possibilities occur when $n=3$, we will consider also the cases
$n=4,5$ both with $m=3,4$. Models with left-right symmetry, horizontal
symmetries and the possible embedding in a larger group (grand unification
scenarios) are briefly discussed.
