An "Old World warbler" is the name used to describe one of a large group of birds that used to be in the bird family Sylviidae. The family held over 400 species in over 70 genera, and was the source of much taxonomic confusion. Two families were separated later, the Cisticolidae and the Regulidae. In the past ten years they have been researched and many species are now put into other families. These families include the Acrocephalidae, Cettiidae, Phylloscopidae, and Megaluridae.