Natural World is a nature documentary television series broadcast annually on BBC Two and regarded by the BBC as its flagship natural history brand. It is currently the longest-running series in its genre on British television, with more than 400 episodes broadcast since its inception in 1983. Natural World is produced by the BBC Natural History Unit in Bristol, but individual programmes can be in-house productions, collaborative productions with other broadcasters or films made and distributed by independent production companies and purchased by the BBC. Natural World programmes are often broadcast as PBS Nature episodes in the USA. Since 2008, most Natural World programmes have been shot and broadcast in high definition.