Warm inflation is comprised of non-isentropic expansion in the background cosmology and thermal seeds of density perturbations. Within the warm inflation regime, while the scale factor undergoes inflationary expansion, the radiation energy density is still substantial due to its constant production from conversion of vacuum energy. This expansion regime is intrinsically different from the supercooled inflation regime, since in the warm inflation case the inflationary period smoothly terminates into a subsequent radiation dominated regime, without a reheating period. I will present an elementary overview of warm inflation. Firstly the background Friedmann cosmology will be derived. Then this cosmology will be motivated from a large class of field theory models. Some results will be presented on expansion e-folds and density perturbations. Next I will describe the elementary origin of dissipation in quantum mechanics and explain the general consistency of warm inflation with dissipative dynamics. Finally a quantum field theory derived warm inflation model will be discussed.