Structural descriptions of viral particles are key to our understanding of their assembly mechanisms and properties. We will describe the application of X-ray crystallography and electron cryomicroscopy to the structural determination of the bluetongue virus core and the herpesvirus capsid. These represent the highest resolution structural studies carried out by these techniques on such complex and large icosahedral virus particles. The bluetongue virus core consists of two layers of distinct proteins with different protein packing symmetries, while the herpes virus capsid is made up of four types of proteins with 3.3 MDa per asymmetric unit. The structural results reveal that each of these proteins has distinct folds and they are packed uniquely to form stable particles.