  A high-energy lepton-lepton collider will give us a unique possibility to
study e-gamma and gamma-gamma interactions at high energies. The high-energy
photons can be generated by Compton back-scattering of laser light on the
high-energy lepton beams. With slightly reduced luminosities for e-gamma and
gamma-gamma collisions compared to the lepton-lepton collider one, unique and
complementary studies can be performed. A linear lepton-lepton collider also
offers other photon sources that will be considered. We will focus on the
complex properties of the photon itself and discuss some possibilities to gain
new insight in its interactions at high energies and how to reveal the
structure of it.
