The omertà is a popular attitude, common in areas of Italy but is especially strong among the Sicilians and where the Mafia is strong. Omertà implies never collaborating with the police. It can be intended also as a vow of silence among mafiosi. A common definition is the "law of silence".

It is common in such areas that, after a Mafia-related murder, people will behave as though they are not able to remember hearing or seeing anything, and no one will be willing to talk to the police.

The origin of the word is often traced to Spanish, meaning manliness. In English, it is often rendered omerta, without an accent.

Among Italian Mafia members, it means that they will not involve the police or the government in the affairs of the Italian Mafia, and will deny its very existence. Joe Valachi was the first person to betray the omertà when in 1963 he publicly spoke out about the existence of the Mafia, when he testified before the United States Congress. Within Mafia culture, breaking the oath of omertà is punishable by death.

Omertà likely influenced the recent movement of Stop Snitchin', which works the very same way.