Digital signatures vs. MACs

From CRYPTUTOR

A digital signature is a public key MAC. That is, the key to verify the signature is not the same as the one used to sign it, and as such may be given out publicly, allowing anyone to verify the signature. This allows new uses for digital signatures that MAC's could not provide, such as non-repudiation. MAC's can only be used between two trusted parties to ensure that no one is interfering with the communication channel, whereas digital signatures may be used to sign a message that is then placed in the public domain.