The combination of wide-ranging spatial and temporal scales associated with the oceanic environment, together with processes intrinsic to the biology of marine organisms, makes the quantitative study of population connectivity a formidable challenge. Sampling over all scales, except for targeted field efforts that focus on selected processes of life stages in limited domains, is presently not possible (Gawarkiewicz et al., this issue). As such, modeling approaches that simultaneously include key physical dynamics and biological traits provide a way forward to investigate general ecological questions as well as provide qualitative assessments regarding connectivity of specific regions and populations (Cowen et al., 2000, 2006; Werner et al., 2001a). In some instances, model results have provided information of relevance to decision-makers in determining marine protected areas and other management strategies (Fogarty and Botsford, this issue). At a minimum, models can be used to generate hypotheses for empirical studies. Overall, coupled biological-physical models are critical tools for addressing the complex processes driving population connectivity in marine systems.