  We discuss the theory and implementation of the finite temperature coupled
cluster singles and doubles (FT-CCSD) method including the equations necessary
for an efficient implementation of response properties. Numerical aspects of
the method including the truncation of the orbital space and integration of the
amplitude equations are tested on some simple systems, and we provide some
guidelines for applying the method in practice. The method is then applied to
the 1D Hubbard model, the uniform electron gas at warm, dense conditions, and
some simple materials. The performance on model systems at high temperatures is
encouraging: for the 1-dimensional Hubbard model FT-CCSD provides a
qualitatively accurate description of finite-temperature correlation effects
even at $U = 8$, and it allows for the computation of systematically improvable
exchange-correlation energies of the warm, dense UEG over a wide range of
conditions. We highlight the obstacles that remain in using the method for
realistic {\it ab initio} calculations on materials.
