The two themes of the Fourth European Symposium on Marine Biology, which took place in Bangor, North Wales, in September 1969, were Larval Biology and Light in the Marine Environment. Originally published in 1971, this volume of edited proceedings from the symposium gives specialist information on the behaviour and structure of larvae of animals that attach themselves to rocks, pilings, ships' hulls, etc. The biology of these organisms is important, both in relation to ship fouling and to mariculture (farming of the sea). It is the larval stage that is vitally important because this is the disseminating phase which enables the organism to find a suitable habitat. The second part of the volume is concerned with the measurement of light in the sea and its effect on the growth of marine algae, and on the behaviour and reproduction of marine animals.