This work synthesizes the current state of knowledge on the biology of polar benthic marine algae and presents an outlook on their responses to changing environmental conditions in polar regions. Topics treated include environment, biodiversity and biogeography of micro- and macroalgae, including an update of the knowledge of the red algal flora of Antarctica. It treats the chemical ecology as well as the primary production and ecophysiology of polar benthic algae with new information on the important contribution of benthic microalgae to the productivity in costal areas.