The origin of the town's name is not fully known. In terms of the original name, "Bissei," an early theory in Reverend J.B. Johnstone's book "The Place-Names of England and Wales" states that it may have meant "Byssa's Isle," and it started life as a lake-village surrounded by marshes, streams and lakes. A more modern theory (but less romantic) is that it is simply derived from the Old English word "bysċe" ("bush, thicket") and Old French "boisseie", meaning a 'place covered with wood'. The latter theory could prove more apt, as the town is located in the valleys which extend southwards from the Chiltern Hills, which were once covered in dense forests of oak, elm, ash, hazel and juniper.