The WHO Recommended Classification of Pesticides by Hazard has been published since 1975, has been revised and reissued every few years and has gained wide acceptance. This document sets out a classification system to distinguish between the more and the less hazardous forms of selected pesticides based (mainly) on acute risk to human health (that is the risk of single or multiple exposures over a relatively short period of time). It takes into consideration the toxicity of the technical compound and its common formulations. The book lists common technical grade pesticides and recommended classifications together with a listing of active ingredients believed to be obsolete or discontinued for use as pesticides, pesticides subject to the prior informed consent procedure, limitations to trade because of the POPs convention, and gaseous or volatile fumigants not classified under these recommendations. This book replaces the 2000-2002 edition of the "Classification." For this latest revisions the WHO Hazard Classes have been aligned with the Acute Toxicity Hazard Categories of the Globally Harmonized System of Classification and Labelling of Chemicals (GHS) as the starting point for allocating pesticides to a Hazard Class. The GHS (as published by an expert committee of the United Nations since 2002) is now being widely used for the classification and labeling of chemicals worldwide. For this revision of the Classifications the GHS Acute Toxicity Hazard Category for each pesticide has been presented alongside the existing information. Part I describes the overarching principles for the classification of pesticides as recommended by the World Health Assembly. These principles continue to apply, but the World Health Assembly Resolution envisaged that the classification criteria might need to be developed with time and increasing experience. The guide-points originally proposed in 1975 are now being aligned with the corresponding Acute Toxicity Hazard Categories from the Globally Harmonized System of Classification. As has always been the case, the classification of some pesticides has been adjusted to take account of severe hazards to health other than acute toxicity. Part II provides guidelines to Classification. Individual products are classified in a series of tables according to the oral or dermal toxicity of the technical product. The tables are subject to review periodically. The latest tables also present the GHS Acute Toxicity Hazard Category for each pesticide. To assist in the classification of formulations, an annex is provided giving numerical tables from which the classification may also be derived.