It is a robust crab of a reddish-brown colour, having an oval carapace with a characteristic "pie crust" edge and black tips to the claws.

It is the subject of the largest crab fishery in Western Europe, centred on the coasts of the Ireland and Britain, with more than 60,000 tonnes caught annually.

It occasionally bears white patches, and is shaped along the front edge into nine rounded lobes,[1] resembling a pie crust.

[4] The first pereiopod is modified into a strong cheliped (claw-bearing leg); the claw's fingers, the dactylus and propodus, are black at the tips.

[1] The other pereiopods are covered with rows of short stiff setae; the dactylus of each is black towards the tip, and ends in a sharp point.

[4] Reproduction occurs in winter; the male stands over the female and forms a cage with his legs protecting her while she moults.

[2] The first developmental stage after hatching is a planktonic larva (1 mm) called the zoea that develops into a postlarva (megalopa), and finally a juvenile.

Juveniles settle to the sea floor in the intertidal zone, where they stay until they reach a carapace width of 60–70 mm (2+3⁄8–2+3⁄4 in), and then migrate to deeper water.

[10] A number of sessile animals occasionally settle as epibionts on the exoskeleton of C. pagurus, including barnacles, sea anemones, serpulid polychaetes such as Janua pagenstecheri, bryozoans, and saddle oysters.

[5] Minimum landing sizes (MLSs) for C. pagurus are set by both the European Union technical regulations and by the UK government.

[13] Recent studies have shown that edible crabs are negatively affected by electromagnetic fields emitted from sub-sea power cables around offshore wind farms.

[18] The specific epithet pagurus is a Latin word, deriving from the Ancient Greek: πάγουρος (pagouros), which, alongside κάρκινος (karkinos), was used to refer to edible marine crabs; neither classical term can be confidently assigned to a particular species.