If by chance, though an increasingly rare one, you find octopus at your fishmonger, don't hesitate to buy it. However, choose one that still has some brown highlights. Other factors to consider:

• The body should be thick, shiny, almost viscous.
• The flesh of the tentacles should be pearly with firm tips.
• The suction cups should produce light suction when you put your finger on them.
• Avoid older males, which are tougher, especially with common octopus.
• Then there's the smell: they should have a briny smell but with no acidity.

Ensure your fishmonger has cleaned out the pouch. The black ink contained in the pouch is edible and can be used to color and flavor sauces and pastas. Ask the fishmonger to keep it for you unless you plan to clean the octopus yourself.

Common octopus, with two series of suction cups on each tentacle, is generally most in demand. However, white octopus, which has only one row of suction cups, has tenderer meat. 

Octopus is also available frozen. It may also be sold cooked sous-vide or in jars, depending on use.

When it comes to quantity, keep in mind that octopus shrinks a great deal when cooked, so allow 1-2 kg for 4 people. 

Octopus should be consumed within 24 to 48 hours of purchase. Otherwise, it can be frozen. The advantage of freezing is that it makes the octopus more tender. See hints and tips from Carme. 

If you buy a fresh whole octopus, you can either leave it whole, or separate the body from the tentacles by halving it under the eyes and mouth. In either case, you have to turn the head inside out like a pillowcase and remove all the contents. Discard the viscera but keep the ink pouch. Then remove the beak and pull the skin off the head and tentacles. Rinse several times between each operation.

The flesh too often tends to be rubbery - to avoid this unpleasant texture, the octopus should be well pounded to tenderize it before any kind of cooking.

For better cooking, it's best to cut the head into rings and to separate the tentacles. Why? Because the tentacles require longer cooking. You've no doubt noticed that some pieces are more tender than other - and that's the reason.

Some chefs cut the tentacles on the diagonal for greater tenderness, while others marinate them with pieces of papaya or kiwi, but here's a technique that is tried and true:
 

Buy an octopus weighing between 2 and 3 kg (4-1/2 to 6-1/2 lb.) Clean it and place in the freezer for a week. Let it thaw slowly to obtain a finer texture: in this way you'll save yourself the long tedious job of pounding it.

In 4 litres (1 gallon) of water, bring the octopus to a boil with some sea salt, a drizzle of olive oil and an onion; boil for one hour. 
 

For the reason mentioned above, the tentacles should be put into boiling water first and blanched with a little salt for 10 minutes to give them some extra cooking time. Then the rings can be added and everything cooked for 30-50 minutes longer. In this way, all the pieces will be perfectly cooked.

To check for doneness, stick a fork into the flesh - if it goes in easily, the octopus is cooked. 

Greece
Octopus is simply grilled or stewed, uncovered, for an hour with olive oil, onions, garlic, tomatoes, bay leaves, orange zest, allspice berries and a little white wine vinegar.

Japan
Octopus is served as sushi. Takoyaki, literally grilled octopus, is a specialty of Osaka, and consists of dough balls containing pieces of octopus, cooked in a special mold. 

Madagascar
Octopus is cooked in a court-bouillon flavored with a carrot, a small onion, a bay leaf, 2 cloves and 6 black peppercorns over low heat for a good hour and a quarter. Cut up the octopus, soak in a good marinade and cook on the grill.

Seychelles
Cook the octopus in water. Drain and cut into pieces. Put some oil into a large saucepan; add a little garlic, ginger, saffron, garam masala, a few cinnamon leaves, salt, pepper and the octopus; cover with coconut milk and simmer for 15 minutes before serving.