Bacteriophages may play ecological key roles in the complex marinebacterial communities and habitats. It is assumed that phages controlbacterioplankton through their lytic activities, and temperate phagesmay contribute to horizontal gene transfer. However, these statementsrely on a limited set of data. Current knowledge is based on microscopicvirus like particle (VLP) counts and some observations using classicalplaque forming units (PFU) providing information of bacteriophages inselected marine habitats. Molecular approaches were applied rarely.Unfortunately, the required infomations in order to decipher the complexpuzzle(s) are presently not available. There is no technique on-hand forquick virus determination. Furthermore, the dominant bacterial hostsare often not culturable. The development of a concept on the systema-tic elucidation of phage ecology is overdue. It should encompass mole-cular and classical approaches. This paper contributes some ideas tosolve these problems.