  We prove Langlands functoriality for the generic spectrum of general spin
groups (both odd and even). Contrary to other recent instances of
functoriality, our resulting automorphic representations on the general linear
group will not be self-dual. Together with cases of classical groups, this
completes the list of cases of split reductive groups whose L-groups have
classical derived groups. The important transfer from GSp(4) to GL(4) follows
from our result as a special case.
