1,2,3-Benzotriazoles could undergo ring cleavage to form ortho-amino arenediazonium or α-diazo-imine species via a Dimroth-type equilibrium. Historically, the synthetic potential of this unique reactivity had remained underdeveloped. Recently, some new strategies have been developed to effect the ring-opening chemistry of benzotriazoles in more practical manners. A wide range of conceptually novel and synthetically useful reactions have been developed, which enable the access to diverse valuable heterocycles and ortho-amino arene derivatives. As one of the players in this field, our group has also contributed a series of intriguing transition-metal-catalyzed denitrogenative functionalizations of benzotriazoles. In this account, we aim to provide an overview of the ring-opening chemistry of benzotriazoles, with a focus on relevant works published in the past decade. In order to show a whole picture of the research field, some pioneering works in its developing history will also be discussed briefly.