自然垄断（Natural Monopoly）指因产业发展的自然需要而形成的垄断状态。如果自然垄断已形成，垄断者便享有巨大的价格竞争力和优势。由于余量需求已被完全满足或进入产业所需投资过巨，没有其他企业会愿意或有能力进入这个无利可图的市场。

一般来说，规模经济能够形成自然垄断，像有些公用工程如供应自来水、电力、通信的企业，投资很大，涉及面很广而利润不宜过高，一个地区设多套自来水管道或电力电讯线路也确显浪费，这种情况即自然垄断。只由一间电力公司提供电力，可以透过大量生产降低发电成本，引入竞争反导致价格上升。又如一个小乡镇，只有一家租车店或一家洗衣店就足以覆盖服务需要，也属自然垄断；再如高科技产品，由于投入资源而形成的技术研发能力，在一定时期只有一家或少数厂家能够生产，而形成自然垄断。

A natural monopoly is a monopoly in an industry in which high infrastructural costs and other barriers to entry relative to the size of the market give the largest supplier in an industry, often the first supplier in a market, an overwhelming advantage over potential competitors. This frequently occurs in industries where capital costs predominate, creating economies of scale that are large in relation to the size of the market; examples include public utilities such as water services and electricity. Natural monopolies were discussed as a potential source of market failure by John Stuart Mill, who advocated government regulation to make them serve the public good.