Balbinus (Latin: Decimus Caelius Calvinus Balbinus Pius Augustus; c. 165 – 29 July 238), was Roman Emperor with Pupienus for three months in 238, the Year of the Six Emperors.

Not much is known about Balbinus before his elevation to emperor. It has been conjectured that he descended from Publius Coelius Balbinus Vibullius Pius, the consul ordinarius of 136 or 137, and wife Aquilia. If this were true, he was also related to the family of Q. Pompeius Falco, which supplied many politicians of consular rank throughout the 3rd century, and to the 1st-century politician, engineer and author Julius Frontinus, as well as a descendant of a first cousin of Trajan. He was a patrician from birth, and was the son (either by birth or adoption) of ... Caelius Calvinus, who was legate of Cappadocia in 184. He was one of the Salii priests of Mars. According to Herodian he had governed provinces, but the list of seven provinces given in the Historia Augusta, as well as the statement that Balbinus had been both Proconsul of Asia and of Africa, are likely to be mere invention. He had certainly been twice consul; his first consulate is not certainly known but is believed to have been about 203 or in July 211; he was consul for the second time in 213 as colleague of Caracalla, which suggests he enjoyed that emperor's favour.

The Roman emperor was the ruler of the Roman State during the imperial period (starting at about 27 BC). The Romans had no single term for the office although at any given time, a given title was associated with the emperor. If a man was "proclaimed emperor" this normally meant he was proclaimed augustus, or (for generals) imperator (from which English emperor ultimately derives). Several other titles and offices were regularly accumulated by emperors, such as caesar, princeps senatus, consul and Pontifex Maximus. The power of emperors was generally based on the accumulation of powers from republican offices and the support of the army.

Roman emperors refused to be considered "kings", instead claiming to be leaders of a republic, however nominal. The first emperor, Augustus, resolutely refused recognition as a monarch. Although Augustus could claim that his power was authentically Republican, his successor, Tiberius, could not convincingly make the same claim. Nonetheless, the Republican institutional framework (senate, consuls, magistracies etc.) was preserved until the very end of the Western Empire.