Coregonid fishes are the forage base in many ecosystems in the northern hemisphere and they have traditionally been part of commercial and native fisheries. Coregonids display extreme variability in morphology, life history, and behavior. Defining boundaries among coregonid taxa has been (and continues to be) the focus of many studies. Cytogenetic, biochemical, and molecular methods have been used to study the 'coregonid problem'. A survey of the literature reveals that questions of taxonomy, followed by phylogeography are most often studied. Sample collections have occurred throughout a representative portion of the coregonid range. The whitefish species Coregonus clupeaformis and C. lavaretus are most often studied. This was expected however because they are the most widely distributed, display the most variation, and are the most commercially important. However, species with restricted ranges such as the Irish pollan (C. pollan) or omul (C. migratorius) have also been studied intensively. Genetic methods have provided insights into several issues, including the placement of Stenodus and the status of C. clupeaformis and C. lavaretus. More recently, studies of sympatric forms over broad geographic scales shed light on processes involved in the evolution of the group and suggest different approaches for management and designation of taxa. ?? 2007 E. Schweizerbart'sche Verlagsbuchhandlung.