In the interest of furthering the understanding of hemodynamics, this study has developed a method for modeling fluid mechanics behavior in individual human carotid arteries. A computational model was constructed from magnetic resonance (MR) data of a phantom carotid bifurcation model, and relevant flow conditions were simulated. Results were verified by comparison with previous in vitro experiments. The methodology was extended to create subject-specific carotid artery models from geometry data and fluid flow boundary conditions which were determined from MR and phase contrast MR (PCMR) scans of human subjects. The influence of subject-specific boundary conditions on the flow field was investigated by comparing a model based on measured velocity boundary conditions to a model based on the assumption of idealized velocity boundary conditions. It is shown that subject-specific velocity boundary conditions in combination with a subject-specific geometry and flow waveform influence fluid flow phenomena associated with plaque development. Comparing a model with idealized Womersley flow boundary conditions to a model with subject-specific velocity boundary conditions demonstrated the importance of employing inlet and flow division data obtained from individual subjects in order to predict accurate, clinically relevant, fluid flow phenomena such as low wall shear stress areas and negative axial velocity regions. This study also illustrates the influence of the bifurcation geometry, especially the flow divider position, with respect to the velocity distribution of the common carotid artery on the development of flow characteristics. Overall it is concluded that accurate geometry and velocity measurements are essential for modeling fluid mechanics in individual human carotid arteries for the purpose of understanding atherosclerosis in the carotid artery bifurcation.