First published in 1971 this volume claims that nitration is important for two reasons. First, because it is the most general process for the preparation of aromatic nitro-compounds, and secondly, on account of the part it has played in the development of theoretical organic chemistry. The special concern of this monograph is with those nitrating systems in which mechanistic studies have established, or made probable, the identity of the agent through which they effect nitration. It presents a summary of the understanding of the nitration process. A discussion of the various types of nitrating systems leads to the conclusion that nitration is generally effected through the nitronium ion. The mechanism of the substitution is examined, and discussed in terms of reactivity for particular groups of aromatic compounds.