Synopsis Bihar, one of the largest states in the country with its dense forests has not been fully explored for its plant wealth. The Botanical Survey of India undertook District Flora Project in 1982 at all-India level. Under this project, five districts of Bihar, namely Dumka, West Champaran, Hazaribagh, Palamau and Giridhi were allotted to different University experts. The present work is the outcome of both extensive and intensive botanical explorations in the district of West Champaran and of a critical evaluation of the flora. In this work, the introdcutory chapter outlines the location, general topographical and climatic features, history of the locality and its people, the past and present botanical surveys, general vegetation types and their floristic composition, economic plants and the phytogeographical considerations of the district. The flora provides a comprehensive coverage of the floristics of the West Champaran district. The taxonomic part deals with keys to the classes, families, genera, species and infra specific taxa. Notes on distribution, frequency, phenology and field collection numbers have been provided for each taxon. Photographs of the location, and the people and line drawings for some important species have been included. Flora of West Champaran District, Bihar is an in-depth scientific study of the flowering plants of the West Champaran district of Bihar. It is to be hoped that this work will be of immense help to students and teachers of botany, foresters, environmentalists, conservationists and persons concerned with raw plant materials for industry alike and will also richly contribute for writing up of the state flora of Bihar with changing needs and new challenges.