Many marine invertebrates form strong, temporary attachments using viscoelastic gels. To better understand these adhesives, an analysis of what is known of gel structure and function was performed. There are different ways of making gels, ranging from entangling of giant glycoproteins to crosslinking of smaller proteins. The mechanics of the gel depend largely on the size of the polymer, its concentration, and whether it is crosslinked. Compared to gels such as mammalian mucus, the mechanics of adhesive mucous gels often appear to depend more heavily on relatively small proteins than on megadalton-sized glycoproteins. In addition, changes in concentration and the presence of specific proteins have been associated with the change from a non-adhesive to an adhesive form. The attachment strengths produced by different gels at different concentrations were compared with the changes in attachment strength seen in living animals. These data suggest that changes in concentration are not sufficient to account for adhesion. Thus, it is likely that the changes in protein composition may play a large role.