Computer simulations of molecular systems are a vital component of modern chemistry and physics. They are being used, for example, in such diverse areas of research as the fundamental physics of crystal nucleation, through to the design of new pharmaceutical entities. Research in the Essex group focuses on innovation in the application of computer simulations to biological systems, where there is the potential to contribute to drug discovery and the development of medical diagnostics. A key challenge restricting success has been limitations in the range of applicability of these computational methods, and in the extent to which accurate predictions may be made. To address these issues, a cross-disciplinary approach that develops new methodologies and deploys these over more realistic systems is used. To test their new simulation methodologies, the Essex group collaborates extensively with academic and industrial partners, both within the UK and internationally. They work not only on small-molecule pharmaceutical development, but also antibody structure, function and design, and drug delivery systems.