Influenza virus is a major human pathogen that binds to cell membranes and infects them through a process of membrane fusion. We have obtained experimental data showing that influenza binds differently to membranes depending on the amount of cholesterol present. We are preforming molecular dynamics simulations to explain these results and also results where binding and fusion depend on the chemical analogue of cholesterol present. These simulations involve large membrane patches and long timescales because we seek to understand the spatial patterning of the membranes involved in controlling viral binding and subsequent infection. Results of these analyses will be used to interpret our experimental data and yield a unified model of how membrane composition controls viral binding as well as shed light on the physical chemistry of heterogeneous membrane systems.