The most important prerequisite for running any practical class is the supply of material. The first edition claimed to be based on protozoa easily accessible from habitats of central Europe. However, many examples that were portrayed in the sections "Genera and Species" occur world-wide and this is particularly true for marine protozoa and parasites.Drawing is unquestionably the very best way to learn about the structure of an organism (see thepreface to the first edition of this book). The fact that digital cameras are now commonplace means that they can sometimes be used as an adjunct to drawing. A trinocular microscope is by no means essential and, with some digital cameras, perfectly adequate shots can be obtained simply by holding the lens of the camera as close as possible to the eyepiece. Moreover, many digital cameras are able to make short video recordings. These can be of very great use when transitory events are recorded and later viewed, perhaps several times, to elucidate a sequence of events. Digital recordings, resulting in still or moving pictures, have other significant advantages, namely that the results can be seen immediately (there is no need to wait for developing and printing) and the availability of the ubiquitous computer leads to both a significant reduction in cost and the ability to share images at no cost.We retained the term "protozoa" because the organisms treated are predominantly unicellular heterotrophic eukaryotic microorganisms with the ability to phagocytose, as weil as coloured euglenids and dinoflagellates which , according to the theory of endosymbiosis, evolved from phagocytosing protozoan hosts with algal endosymbionts. A chapter on marine planktonic diatoms is now included because diatoms occur in most plankton sampies. All of the organisms treated here are also protists (see definition below). However, the user of a textbook entitled "A course in protistoloqy" would expect to find more unicellular algae and lower fungi included. Most of our authors have used the system given in the second edition of the IIlustrated Guide to the Protozoa (Lee et al. 2000), while others have preferred the system of Cavalier-Smith (1998, 2003). For algae, the textbook of van den Hoek, Mann &Jahns (1995) has been followed.A bibliography at the end of each chapter contains important original papers, review articles, monographs, available literature for identification, and scientific filrns. Textbooks are listed at the end of the book in front of the index.