The 2nd century is the period from AD 101 (represented by the Roman numerals CI) through AD 200 (CC) in accordance with the Julian calendar. It is considered part of the Classical era, epoch, or historical period.

Early in the century, the Roman Empire attained its greatest expansion under the emperor Trajan, but after his death became primarily defensive for the rest of its history. Much prosperity took place throughout the empire at this time, ruled as it was by the "Five Good Emperors", a succession of well-received and able rulers. This period also saw the removal of the Jews from Jerusalem during the reign of Hadrian after Bar Kokhba's revolt.

The last quarter of the century saw the end of the period of peace and prosperity known as the Pax Romana at the death of the emperor Marcus Aurelius, last of the "Five Good Emperors", and the ascension of Commodus. After Commodus was murdered in 192, a turbulent period known as the Year of the Five Emperors ensued. After the quick successive removals of Pertinax and Didius Julianus from power, this period had the general-turned-emperor Septimius Severus, who was the founder of the Severan dynasty, pitted against rival claimants in the form of Pescennius Niger. Severus' forces defeated the rival claimants at the Battle of Issus in 194, and Clodius Albinus, whom he defeated at the Battle of Lugdunum in 197, granting Severus sole authority over the empire.

Although the Han dynasty of China was firmly cemented into power and extended its imperial influence into Central Asia during the first half of the century, by the second half there was widespread corruption and open rebellion.