The halogenated phenols and anilines are the parent chromophores of a number of widely used pesticides, among them phenoxyacetic acid and phenylurea derivatives, and of other biocides. The direct photolysis of the substances in the environment has become a subject of increasing interest. In the first part of this review, investigations of the photochemistery of halogenated phenols and anilines carried out during the last decade are summarized. The second part is concerned with corresponding studies on biocides. The phototransformation mechanisms of these compounds have been found to share many common features. In particular, two kinds of heterolytic dehalogenation processes, aromatic carbon-halogen photohydrolysis on the one hand and formation of triplet carbenes or aryl cations on the other, have been described for many systems. The mechanistic knowledge gained in the investigations of model compounds is increasingly brought to bear on actual environmental situations.