Intensive quenching (IQ) is an alternative method of hardening steel parts, providing extremely high cooling rates within the martensite-phase formation temperature range. This article begins with the description on the general correlation between steel mechanical properties and cooling rate during IQ. It presents a review of batch intensive quenching (IQ-2) methods and single-part intensive quenching (IQ-3) methods as well as practical applications of these methods. The article provides useful information on the effect of heat flow on cooling in these methods, and discusses the improvements achieved in part microstructure, mechanical properties, and stress conditions of steel, after intensive quenching. It also describes the reasons for part distortion in IQ, and reviews the types of quench systems used in IQ-2 and IQ-3 processes.