The current classification of the Arthoniales and phylogenetic hypotheses for the order are discussed. The available phylogenetic analyses of the order lead to a better understanding of certain groups, particularly the Roccellaceae and Chiodecton sensu lato. However, numerous genera in these groups contain a low number of species, whereas the majority of the ca 1,200 species in the order is found in only three genera: Arthonia, Arthothelium and Opegrapha. Other formerly large genera e.g., Schismatomma, Lecanactis, and Chiodecton, have already been split into smaller units, but the classification of Arthonia and Arthothelium is still unsettled. A phylogenetic analysis is included to elucidate the position of Cryptothecia, Chrysothrix, and additional species of Arthonia and Arthothelium in the order. Selected morphological characters used in the classification and phylogeny of the Arthoniales are reviewed and a key to the better known genera is presented. With approximately 1,200 species, and about 61 genera (Hawksworth et al. 1995), the Arthoniales are one of the largest groups of mainly lichenized fungi. Originally, the Arthoniales were described as an order separate from the Opegraphales (Hawksworth & Eriksson 1986) but today it is commonly accepted that the Opegraphales are included in the Arthoniales. During the last two decades, considerable progress in classification within the Arthoniales has been achieved. Many studies have resulted in generic rearrangements and led to smaller and supposedly more 'natural' genera. On the other hand, relationships between genera and the delimitation of families have remained controversial. Significantly, more than 50% of the genera have an uncertain position within the order according to a recent classification of lichenized fungi (Tehler 1996). In the first part of the paper, an overview is given on the current taxonomic and phylogenetic concepts within the order. This is followed by a discussion of selected characters, which are also used in the key to genera in the last part of this contribution. THE POSITION OF THE ARTHONIALES IN THE