Many protein interactions are mediated by small protein modules binding to short linear peptides. DOMINO (http://mint.bio.uniroma2.it/domino/) is an open-access database comprising more than 3900 annotated experiments describing interactions mediated by protein-interaction domains. DOMINO can be searched with a versatile search tool and the interaction networks can be visualized with a convenient graphic display applet that explicitly identifies the domains/sites involved in the interactions.