Compounds of the (2H)-1,4-benzoxazin-3(4H)-one class have attracted the attention of phytochemists since the first isolation of 2,4-dihydroxy-2H-1,4-benzoxazin-3(4H)-one (DIBOA) and 2,4-dihydroxy-7-methoxy-(2H)-1,4-benzoxazin-3(4H)-one (DIMBOA). Extensive research has been carried out on the isolation and synthesis of these materials as well as on the dynamics of their degradation in different systems. This has led to the discovery of a wide variety of compounds that are of high interest from the point of view of phytotoxic, antifungal, antimicrobial, and antifeedant effects among others. The potential application of benzoxazinones and their derivatives as leads for natural herbicide models is a topic of current interest. Furthermore, the importance of degradation on the ecological behaviour of benzoxazinone-producing plants is also being realised, and proposals concerning the role of the degradation products in chemical defence mechanisms have been put forward. There is also increasing interest in the improvement of analytical methodologies, and ecotoxicologic effects, toxicity on target and non-target organisms, and degradation kinetics are also being addressed. The development of new phytotoxicity bioassay techniques represents one of the most important breakthroughs in this respect. Moreover, benzoxazinones and some of their derivatives have been employed in the development of pharmaceuticals. The versatility of the benzoxazinone skeleton, in addition to its relative chemical simplicity and accessibility, makes these chemicals amongst the most promising sources of bioactive compounds that are natural in origin.