Bretherick's Handbook of Reactive Chemical Hazards, Fourth Edition, has been prepared and revised to give access to a wide and up-to-date selection of documented information to research students, practicing chemists, safety officers, and others concerned with the safe handling and use of reactive chemicals. This will allow ready assessment of the likely potential for reaction hazards which may be associated with an existing or proposed chemical compound or reaction system. A secondary, longer-term purpose is to present the information in a way which will, as far as possible, bring out the causes of, and interrelationships between, apparently disconnected facts and incidents. This handbook includes all information which had become available to the author by April 1989 on the reactivity hazards of individual elements or compounds, either alone or in combination. It begins with an introductory chapter that provides an overview of the complex subject of reactive chemical hazards, drawing attention to the underlying principles and to some practical aspects of minimizing such hazards. This is followed by two sections: Section 1 provides detailed information on the hazardous properties of individual chemicals, either alone or in combination with other compounds; the entries in Section 2 are of two distinct types. The first type of entry gives general information on the hazardous behavior of some recognizably discrete classes or groups of the 4,600 or so individual compounds for which details are given in Section 1. The second type of entry concerns reactive hazard topics, techniques, or incidents which have a common theme or pattern of behavior involving compounds of several different groups, so that no common structural feature exists for the compounds involved.