  We study the question of generalizing light-front field theories to finite
temperature. We show that the naive generalization has serious problems and we
identify the source of the difficulty. We provide a proper generalization of
these theories to finite temperature based on a relativistic description of
thermal field theories, both in the real and the imaginary time formalisms.
Various issues associated with scalar and fermion theories, such as
non-analyticity of self-energy, tensor decomposition are discussed in detail.
