  I present a case for proposed future linear and circular lepton colliders as
ideal machines for understanding and exploration. As machines for
understanding, they provide unprecedented tools for studying the Higgs and
observing phenomena never before seen in nature. As machines for exploration,
they are ideally suited to discovering new particles interacting too weakly to
be seen otherwise. These arguments for future lepton colliders are largely
independent of the as-yet-unknown outcome of the LHC physics program.
