Recent advances in ultrastructural and molecular research have provided new understandings of relationships of traditional chrysophytes, and also many new genera have been described in the last two decades. In this encyclopedia 201 genera of chrysophytes known to date (plus numerous synonyms) are surveyed, namely 110 genera of Chrysophyceae sensu stricto and 58 additional genera, many of which have previously been accommodated in the Chrysophyceae, but are now placed in other classes of the Chromophyta/Heterokonta [i.e., Synurophyceae (8 genera), Dictyochophyceae (13 genera), Pelagophyceae (10 genera), Phaeothamniophyceae (16 genera) and "Bicosoecophyceae" (11 genera)]. Also treated are 33 insufficiently known genera of uncertain affinity, which probably do not belong to the Chrysophyceae sensu stricto, but which have often been assigned to this class (e.g., among others, genera included in the family Aurosphaeraceae and in the orders Chrysomeridales and Parmales). The concept of classification presented in this book is very different from that in the last detailed monographs on freshwater Chrysophyceae by Bourrelly (1981) and Starmach (1985). We also include information on more than 80 genera which have not yet been treated by these authors. Almost 50 of these are marine and are now mostly classified in the Dictyochophyceae, Pelagophyceae and "Bicosoecophyceae", or belonging to the genera of uncertain chrysophyte affiliation. In comparison with these previous monographs a number of colourless flagellates (e.g., the choanoflagellates that were included in the Chrysophyceae as a separate subclass, Craspedomonadophycidae), have been taken away from this class, since they were shown to be related to different protistan lineages with no close relationships to heterokonts. This volume is the result of an ambitious project, entitled "Encyclopedia of Algal genera" launched back in 1988 by Bruce Parker and sponsored by the Phycological Society of America. A large team of coeditors and contributors was set down, so that all groups of algae could be covered. After some years, however, the project ran into difficulties and it became increasingly clear that it could not be completed so that in 1999 it was finally abandoned. The manuscripts, in different states of completeness, were handed over to the Phycological Society of America, who, unfortunately, did not find it possible to continue the project and bring it to conclusion (publication). The chrysophyte manuscripts, however, were almost complete and newly revised, and we found that all our work, together with that of the other chrysophyte contributors, should not be wasted, but published as a separate chrysophyte encyclopedia in Bibliotheca Phycologica. The editors and contributors thank PSA who supported the idea and gave the necessary permissions.