There are two main types. The european lobster, found in British and Norwegian waters, is a violet-blue or greenish colour and has a very delicate flavour. The Northern lobster, fished off the east coasts of Canada and the United States, is said to have less flavour. When cooked, the lobster turns red, which is why it is sometimes called "the cardinal of the seas" (Monselet); it is therefore difficult to distinguish the origins when it is bought cooked from a fishmonger. Although a prolific breeder, the lobster has had to be protected: since 1850 experiments in lobster farming have been carried out on both sides of the Atlantic, but it is still regarded as a rather special delicacy.

A live lobster, which can be identified by the reflex actions of the eyes, antennae, and claws, should show any signs of damage from fighting or have any pieces missing when it is bought, especially if it is to be boiled. A female is generally heavier and better value than a male of the same size and in the opinion of gourmets has a better flavour. An average lobster is about 12 inches (30 cm) long and weighs 3/4 to 1 pound (300 to 500 g). Lobsters can reach a length of 2 1/2 feet (75 cm) and a weight of 5 amd more pounds (serveral kg), but such specimens are very rarely sold on the open market.

The British Universities Federation for Animal Welfare had discovered that lobsters can be humanely killed by putting them in a plastic bag in the freezer (at a temperature at least as low as 14°F or -10°C) for two hours. The lobster will gradually lose consciousness and die. It can be then plunged into boiling water. If a freezer is unavailible, make sure that at least 1 gallon (4.5 liters) water per lobster is boiling fast over a very hot flame before plunging the lobster in head first, insuring it is totally immersed. Hold it under the water with wooden spoons for at least 2 minutes. The loster should die within 15 seconds. If the recipe calls for uncooked lobster, remove it after 2 minutes.