The emission of light by a material at temperature T has been shown recently to be coherent in the near field. These properties were attributed to the thermal excitation of surface polaritons. We review the origin of this phenomenon. We analyze the influence of the microstructure and temperature on the coherence properties and show how to engineer thermoradiative properties of surfaces. We report the design of a quasi-isotropic source and a very directional source of thermal light. We also report a measurement of the transverse coherence length of a thermal source of light. The tungsten filaments of light bulbs are certainly the most widely used sources of light. The microscopic mecha- nism of light generation is the spontaneous emission of a photon when an emitter thermally excited relaxes to a lower state. Such light sources are called thermal sources. They are usually almost isotropic sources of light with a broad spec- trum. This contrasts with a laser that produces very direc- tional and monochromatic light. The narrow spectrum is a measure of the temporal coherence of the source, whereas the directivity is a measure of its spatial transverse coher- ence. Recently, it has been realized 1-3 that a thermal source of light could be coherent in the near field, i.e., when ana- lyzing the light at distances of the surface much smaller than the peak wavelength of the spectrum. Further work has led to the construction of a coherent thermal source of light. 4 It has thus been shown that a source based on spontaneous emis- sion may produce light that is partially coherent, both spa- tially and temporally. In this paper, we shall report a detailed study of this type of source and discuss the role of surface waves in building coherent fields. We will report a measure- ment of the coherence length of the field along the source. We will also carefully study the role of the temperature on the emission. We will finally report measurements on a type of source that produces an isotropic emission of light. The emission of light by hot bodies is usually discussed in