Dinophyceae are an important part of the phytoplankton of marine waters and integral part of the species occuring during phytoplankton- monitoring. Therefore a quality standards for species determination is needed. In fixed samples, as routinely used for phytoplankton monitoring, only thecate dinoflagellates can be identified at genus and species level with some degree of certainty normally athecate dinophyceae cannot be identified in formalin or lugol-fixed samples. For this reason this Identification Help is restricted to thecate dinophyceae with very few exceptions.Well known identification methods are the use of either dichotomous keys or picture books. Both methods have their limitations, and all biologists having used a dichotomous key made the experience of total failure.This Identification Help tries to combine both methods, lumping several taxa with common features and pinpointing at the figures important features for discriminate similar species.Nearly all identification books have the disadvantage, that only part of the relevant species are mentioned or depicted. To overcome this problem a check-list of all species with authors recorded for the area is provided, including the synonyms used in the relevant literature for the area. This will also enable administrators to follow name-changes of relevant taxa in the literature and in reports. Names in bold are those we regard as correct.A general introduction will provide a short overview on morphology and life stages of the species dealt with. A short description and , if necessary, diagrams for each taxonomic group helps to use the following Identification Help. Relevant literature is given as well as information on potentially toxic species. Pictures (line drawings, often from the original description, and photos) enriched with markings to show the most relevant features for identifcation are the main part of this Identification - Help. Warnings are given if species cannot be identified in routine monitoring samples and suggestions for groupings are given.