A natural monopoly is a market situation in which a single firm serves the whole market, therefore it is the only producer of a certain good or service, due to the fact that there exist some natural conditions which establish huge barriers for new competitors entering in the market, in the sense of extremely large fixed costs.
In such a case there is no market competition, therefore the monopoly can decide on the quantity supplied and on the price of the products (usually establishing a much higher one that if there was competition). Such a situation is harmful for consumers. They purchase products at a higher price and with lower quality because, as there is no competition, producers are not forced to continuously develop and improve their products. This is why goverment intervenes, trying to soften the situation by decreasing the profits of the monopolists and increasing the welfare of consumers, and the social welfare.
