The protein-solvent interface is complex and may include solvent chann
els and cavities as well as the normal surface water molecules. We des
cribe several algorithms for investigating the intra- and inter-molecu
lar interactions of proteins in general but with the aim of developing
methods to accurately and definitively characterise the interactions
of water and other small ligands with proteins. Specifically, we prese
nt the methods which underlie three programs (AQUARIUS2, HOLE and PRO_
ACT) which can be used to to look at different aspects of these intera
ctions.