A thorough understanding of planktonic organisms is the first step towards a real appreciation of the diversity, biology, and ecological importance of marine life. A detailed knowledge of their distribution and community composition is particularly important since these organisms are often very delicate and sensitive to change, and can be used as early indicators of environmental change. Natural and man-induced modification of the environment can affect both the distribution and composition of plankton, with important ecological and economic impacts. This book provides a practical guide to plankton biology with a large geographic coverage spanning the North Sea to the north-eastern Atlantic coast of the USA and Canada. The book is divided into three sections: an overview of plankton ecology, an assessment of methodology in plankton research covering sampling, preservation, and counting of samples, and a taxonomic guide illustrated with line drawings to aid identification.