The first review is devoted to the fundamental properties of lead halides and its modern and future applications. Here we deal with electronic properties of these crystals as well as the main peculiarities of lattice dynamics. For the first time was done the experimental proofs of the existence of self-trapped electrons in PbCl2 that was predicted by Landau in 1933. Several specialized topics are treated, including the low temperature study of the fundamental absorption and intrinsic luminescence spectra as well as the processes of the ionic and photoconductivity. The kinetics and the mechanisms of photodecomposition of PbX2 are discussed in detail. A discussion of several significant factors that may complicate the decomposition process is given, with emphasis on purity and conditions of the prepared samples. (C) 2003 Elsevier Ltd. All rights reserved.