Protein adsorption on solid surfaces is widespread in chemical engineering and beyond. It may be a desired phenomenon (e.g. the chromatographic separation of antibodies), but it can also have a negative impact on processes such as in the fouling of the heater surfaces in the milk processing industry. Being able to predict the free energy of adsorption for proteins is essential to the de novo rational design of surfaces and solvents that either enhance or reduce protein adsorption. Whilst methods for estimation of the free energy do exist, they are largely empirical and/or based on sever assumptions. An example of the latter is the assumption that proteins undergo no major conformational change upon adsorption – our prior work (and that of others) clearly shows this is unlikely to be satisfied in general. We have, therefore, developed two methods for estimating the free energy of protein adsorption that avoids this assumption – a computationally expensive but in principle accurate technique based on molecular dynamics (MD) simulation, and a second much quicker technique based on global molecular mechanics that is able to yield estimates that are comparable to those predicted by MD. These two methods will be presented and demonstrated by considering the adsorption of Met-enkephalin at the gas-graphite and graphite-water interfaces.