The widening interest in marine biology has led to the establishment of an increasing number of school and undergraduate courses in the subject. There are many books on various aspects of marine biology which students can read with advantage, but few that are suitable as introductory reading at the commencement of studies. This book has been compiled primarily as an aid for zoology students at the start of a special course on marine biology. The text is an introduction to the author's annual course for undergraduates. The aim has been a concise presentation of information and ideas over the general field of marine ecology, with guidance on the selection of more advanced reading. The sources of further information given at the end of each chapter have been chosen as far as possible from books and journals to which students should have reasonably easy access. These lists provide a selection of additional reading which starts at an elementary level and be­ comes more advanced as the course proceeds. Students entering the author's course are usually in their third under­ graduate year, and a general knowledge of the phyla is therefore assumed.