With the rapid progresses in both instrumentation and computing, it is increasingly straightforward and routine to determine the structures of icosahedral viruses to subnanometer resolutions (6-10 A) by cryoelectron microscopy and image reconstruction. In this resolution range, secondary structure elements of protein subunits can be clearly discerned. Combining the three-dimensional density map and bioinformatics of the protein components, the folds of the virus capsid shell proteins can be derived. This chapter will describe the experimental and computational procedures that lead to subnanometer resolution structural determinations of icosahedral virus particles. In addition, we will describe how to extract useful structural information from the three-dimensional maps.