[en] After a review of solid-state conduction counters, in general, and of the history of mercuric iodide, in particular, the theory of operation of solid-state energy-dispersive HgI₂ detectors is dicusssed. The main factors which limit energy resolution in solid-state compound detectors are considered, including statistical fluctuations in charge generation, the window effect, trapping, inhomogeneities in the detector material, and electronic noise. Potential applications of room-temperature HgI₂ x-ray detectors are listed, and general considerations are discussed for x-ray fluorescence analysis with HgI₂. Directions of current investigations are given