Virus assembly is a remarkable example of macromolecular self-assembly. Viruses encapsulate and release genetic materials at different points of their life cycle. To allow successful capsid assembly and disassembly, virus capsid should be both stable and dynamic. To fundamentally understand these apparently contradictory physical properties, we are using state-of-the-art experimental and theoretical methods, developed in our lab, to perform rigorous and high precision thermodynamic and structural analysis of the assembly process of SV40 or Hepatitis B virus (HBV).