In this review paper we present the most important features of microwave irradiation, their physical characteristics and the properties upon an interaction with matter. The heating mechanisms are described, followed by a description of the available microwave equipment, including the differences between single- and multi-mode microwave reactors, considerations on open vs. closed reaction vessels, the selection of the appropriate solvents (or possible uses of solvent-free reaction conditions), the problems connected with scale-up, as well as the continuous flow processes and automation of microwave-assisted synthesis. A series of transformations of organic compounds with the emphasis on the conversion of heterocycles is presented. In the last part we present some of the most interesting properties of 2H-pyran-2-ones, their fused derivatives and other systems, including the synthesis of natural and other compounds incorporating this structural fragment and further transformations with a special emphasis on Diels-Alder cycloadditions. The research conducted in domestic microwave ovens is, due to the well-known problems associated with reproducibility, only partially included.