Let
G
G
be a classical
p
p
-adic group and let
π
\pi
be a smooth irreducible representation of
G
G
. In this paper, we consider the problem of calculating the dual (in the sense of Aubert and Schneider-Stuhler)
π
^
\hat {\pi }
. More precisely, if
π
\pi
is specified by its Langlands data, the problem is to determine the Langlands data for
π
^
\hat {\pi }
. This problem reduces (based on supercuspidal support) to two main cases: half-integral reducibility and integral reducibility; the latter is addressed here.