Valeria Messalina (22 - 48) was the third wife of the Roman emperor Claudius. She was the daughter of Domitia Lepida (granddaughter of Mark Antony) and Valerius Messalla Barbatus, so of a noble family, and she had been a regular at the court of Caligula.

She married Claudius around 38 A.D. and bore him two children, Britannicus (~39 - 55 A.D.), who might actually have been fathered by Caligula, and Octavia (~41 - 62 A.D.), who married her own stepbrother the emperor Nero. In 48 Messalina conspired to kill Claudius with Caius Silius while her husband was in Ostia. She actually went through a public marriage ceremony with Silius (he was also already married, to Junia Silana); her motivation is believed to have been the protection the powerful and popular Silius could give her over the weakness of Claudius, and her plotting was sufficiently promising that many senior officials were swayed to her side. Exposed by Narcissus, an advisor to Claudius, Messalina, Silius and a number of others were summarily executed. Messalina was apparently offered the opportunity of suicide but was unable to do it.

Her reputation is very poor, a number of Roman historians (mainly Tacitus and Suetonius) portray her as a cruel, avaricious, foolish nymphomaniac who had many wild affairs and duped Claudius and manipulated him into executing those who displeased or spurned her. She is also recorded as a lover of parties and festivities as well as a enthusiastic player of court politics, selling her influence to Roman nobles and foreign notables. Her name is now used as a synonym for others with her supposed vices.

As a wife she succeeded Plautia Urgulanilla and Aelia Paetina. She was in turn replaced by Agrippina the Younger.