This book is a translation of the German edition.15 pictures have been replaced with better ones, and seven species have been added. - The present guide will help in the identification of marine algae (macroalgae, seaweeds) without requiring special knowledge of the subject and technical aids, such as a microscope. For a person interested in nature with a general interest in and knowledge of biology, a direct comparison of seaweed material with the original colour images herein will be useful in recognising the essential morphological chararcteristics of genera and/or species. The acommpanying text is intended to support this, and is essentially reduced to a description of morphological characteristics that can be seen with the unaided eye (although a small magnifying lense is helpful in some cases). This is supplemented by additional information, particularly on habitat and geographical distribution.