Bottom trawling is trawling (towing a trawl, which is a fishing net) along the seafloor. It is also referred to as "dragging". The scientific community divides bottom trawling into benthic trawling and demersal trawling. Benthic trawling is towing a net at the very bottom of the ocean and demersal trawling is towing a net just above the benthic zone. Bottom trawling can be contrasted with midwater trawling (also known as pelagic trawling), where a net is towed higher in the water column. Midwater trawling catches pelagic fish such as anchovies and mackerel, whereas bottom trawling targets both bottom-living fish (groundfish) and semi-pelagic species such as cod, squid, shrimp, and rockfish.

Trawling is done by a trawler, which can be a small open boat with only 30 hp (22 kW) or a large factory trawler with 10,000 hp (7,500 kW). Bottom trawling can be carried out by one trawler or by two trawlers fishing cooperatively (pair trawling).

Global catch from bottom trawling has been estimated at over 30 million tonnes per year, an amount larger than any other fishing method. Concerns about the environmental impacts of bottom trawling have led to changes in gear design, such as the addition of turtle excluder devices to reduce bycatch, and limitations on locations where bottom trawling is allowed, such as marine protected areas. A 2021 paper estimated that bottom trawling contributed between 600 and 1500 million tons of carbon dioxide a year by disturbing carbon dioxide in the sea floor – emissions approximately equivalent to those of Germany, or the aviation industry. However, these values are highly uncertain and have been criticized as overestimates. International attempts to limit bottom trawling have been ineffective.

An early reference to fishery conservation measures comes from a complaint about a form of trawling dating from the 14th century, during the reign of Edward III. A petition was presented to Parliament in 1376 calling for the prohibition of a "subtlety contrived instrument called the wondyrchoum". This was an early beam trawl with a wooden beam, and consisted of a net 6 m (18 ft) long and 3 m (10 ft) wide,

of so small a mesh, no manner of fish, however small, entering within it can pass out and is compelled to remain therein and be taken...by means of which instrument the fishermen aforesaid take so great abundance of small fish aforesaid, that they know not what to do with them, but feed and fatten the pigs with them, to the great damage of the whole commons of the kingdom, and the destruction of the fisheries in like places, for which they pray remedy.

Another source describes the wondyrchoum as:

three fathom long and ten men's feet wide, and that it had a beam ten feet long, at the end of which were two frames formed like a colerake, that a leaded rope weighted with a great many stones was fixed on the lower part of the net between the two frames, and that another rope was fixed with nails on the upper part of the beam, so that the fish entering the space between the beam and the lower net were caught. The net had maskes of the length and breadth of two men's thumbs

The response from the Crown was to "let Commission be made by qualified persons to inquire and certify on the truth of this allegation, and thereon let right be done in the Court of Chancery". Thus, already back in the Middle Ages, basic arguments about three of the most sensitive current issues surrounding trawling – the effect of trawling on the wider environment, the use of small mesh size, and of industrial fishing for animal feed – were already being raised.