Instability of atherosclerotic plaques in carotid artery stenosis is a process of biomechanical failure, governed by the interactions between material properties, microstructural organization, and local stress distributions. Clinical adverse events, including transient ischemic attacks and ischemic stroke, occur when structural stresses within the plaque exceed the local material strength of the tissue. Current risk stratification approaches and treatment decisions rely primarily on stenosis grade and patient symptomatology, but fail to account for the biomechanical characteristics of plaque. This limitation motivates the need for a more mechanics-informed, patient-specific framework in assessing plaque vulnerability. To address this, the current thesis aims to investigate the passive mechanical properties of human carotid plaque obtained through endarterectomy by employing a combination of ex vivo inflation and biaxial testing.