Publius Septimius Geta (7 March 189 – 26 December 211) was Roman emperor with his father Septimius Severus and older brother Caracalla from 209, when he was named Augustus like his brother, who had held the title from 198. Severus died in 211, and although he intended for his sons to rule together, they proved incapable of sharing power, culminating with the murder of Geta in December of that year.
Geta was the younger son of Septimius Severus by his second wife Julia Domna. He was born on 7 March in either Rome or Mediolanum, at a time when his father was only a provincial governor at the service of Emperor Commodus. In 198, Geta was raised to Caesar. Septimius Severus gave him the title of augustus in late 209.

During the campaign against the Britons in the early 3rd century AD, imperial propaganda promoted the image of a happy family that shared the responsibilities of rule. Geta's brother Caracalla acted as Severus' second-in-command, and administrative and bureaucratic duties were Geta's responsibility. In reality, however, the rivalry and antipathy between the brothers did not abate. With the death of Severus in 211, control of the empire passed to Geta and Caracalla jointly.

When Septimius Severus died in Eboracum on 4 February 211, Caracalla and Geta were proclaimed joint emperors and returned to Rome. Their mother, Julia Domna, who had served as a crucial advisor and confidante to her husband, was able to maintain her political influence over two co-emperors. It is said that on the journey from Britain to Rome the two brothers kept well away from each other, not once lodging in the same house or sharing a common meal.

Their joint rule was a failure. The Imperial Palace was divided into two separate sections, and neither allowed the servants of the other into his own. They only met in the presence of their mother, and with a strong military guard, being in constant fear of assassination. The current stability of their joint government was only through the mediation and leadership of their mother, Julia Domna, accompanied by other senior courtiers and generals in the military. The historian Herodian asserted that the brothers decided to split the empire in two halves, but with the strong opposition of their mother, the idea was rejected, when, by the end of 211, the situation had become unbearable. Caracalla tried unsuccessfully to murder Geta during the festival of Saturnalia (17 December). Finally, the next week, Caracalla had his mother arrange a peace meeting with his brother in his mother's apartments, thus depriving Geta of his bodyguards, and then had him murdered in her arms by centurions.

Caracalla ordered the damnatio memoriae, which was thoroughly carried out, as is clear from the archaeological record. Reportedly, Caracalla was thereafter tormented by guilt over his deed, but sought to expiate it by adding to this crime the proscription of all his brother's former followers. Cassius Dio stated that around 20,000 men and women were killed or proscribed on this charge during this time.