Bioadhesion is said to occur when two materials, at least one of which is biological in nature, are held together for extended periods. Bioadhesion includes cell-to-cell adhesion, bacteria binding to surfaces, adhesion to mucous membranes and the use of adhesive materials in medical treatments (such as in drug delivery devices, tissue adhesives or wound dressings). There are two stages in the formation of the bioadhesive joint: The first is the contact stage, when two surfaces are brought together into intimate contact, and the second is the consolidation stage, when the adhesive interactions occur. There are several theories as to how such interactions arise, based around surface “wetting”, macromolecular interpenetration, mechanical interlocking, adsorption, fracturing of the adhesive bond and electron transfer across an interface. The bioadhesion process is usually complex, and requires the application of more than one of these theories. Knowledge of the mechanism of bioadhesion will permit a greater understanding of the processes that happen in the natural world, and allow the development of more effective systems that can be used in medical therapies.