This is a guide on what declawing is so you are fully informed on the surgical procedure.

The medical word for declawing is onychectomy. It is an operation which surgically removes the claws and part of the toes of the cat. This process involves amputating all or part of the end bone, or distal phalanx, of the cat's toes.
To compare:
Distal phalanx of a cat's paw

Distal phalanx of a human hand

Declawing is performed on cats to prevent damage to household possessions such as couches, carpets and curtains by scratching, and to prevent scratching of people. It should be noted that this procedure is more common in North America. Other countries such as England, Italy, Germany, Denmark, Finland, Belgium, Spain, Australia and many more, consider declawing as illegal or is only performed due to medical circumstances.
Medical reasons include chronic inflammatory distal phalanx, tumors, or persistent and severe infections and gangrene, then the procedure is usually limited to the affected claw.

Read about the medical procedure in detail.

Read about complications from the surgery.

Scratching behavior in cats and alternatives to declawing.