Marine microorganisms have become an important point of study in the search for novel microbial products. Today, both academic and industrial interest in marine microorganisms is on the rise, in part because of the growing number of unique, biologically active secondary metabolites reported from marine bacteria. Our ability to assess the biosynthetic potential of marine bacteria, however, is inevitably coupled to our basic understanding of their biology. This review summarizes the chemical discoveries and biological activities reported from marine bacteria and focuses upon several microbiological topics as they relate to natural product discovery, including the distributions, diversity, and culturability of marine bacteria, as well as the role of symbiotic bacteria in the production of substances previously ascribed to other sources.