It is generally established that the unstable plaque is the major cause of acute clinical sequelae of atherosclerosis. Unfortunately, terms indicating lesions prone to plaque instability, such as "vulnerable plaque," and the different phenotypes of unstable plaques, such as plaque rupture, plaque fissuring, intraplaque hemorrhage, and erosion, are often used interchangeably. Moreover, the different phenotypes of the unstable plaque are mostly referred to as plaque rupture. In the first part of this review, we will focus on the definition of true plaque rupture and the definitions of other phenotypes of plaque instability, especially on intraplaque hemorrhage, and discuss the phenotypes of available animal models of plaque instability. The second part of this review will address the pathogenesis of plaque rupture from a local and a systemic perspective. Plaque rupture is thought to occur because of changes in the plaque itself or systemic changes in the patient. Interestingly, contributing factors seem to overlap to a great extent and might even be interrelated. Finally, we will propose an integrative view on the pathogenesis of plaque rupture.