The Migration Period, also known as the Barbarian Invasions, was a period in European history marked by large-scale migrations that saw the fall of the Western Roman Empire and subsequent settlement of its former territories by various tribes, and the establishment of the post-Roman kingdoms. The term refers to the important role played by the migration, invasion, and settlement of various tribes, notably the Franks, Goths, Alemanni, Alans, Huns, early Slavs, Pannonian Avars, Magyars, and Bulgars within or into the former Western Empire and Eastern Europe. The period is traditionally taken to have begun in AD 375 (possibly as early as 300) and ended in 568. Various factors contributed to this phenomenon of migration and invasion, and their role and significance are still widely discussed.

Historians differ as to the dates for the beginning and ending of the Migration Period. The beginning of the period is widely regarded as the invasion of Europe by the Huns from Asia in about 375 and the ending with the conquest of Italy by the Lombards in 568, but a more loosely set period is from as early as 300 to as late as 800. For example, in the 4th century a very large group of Goths was settled as foederati within the Roman Balkans, and the Franks were settled south of the Rhine in Roman Gaul. In 406 a particularly large and unexpected crossing of the Rhine was made by a group of Vandals, Alans and Suebi. As central power broke down in the Western Roman Empire, the military became more important but was dominated by men of barbarian origin.

There are contradictory opinions as to whether the fall of the Western Roman Empire was a result of an increase in migrations, or both the breakdown of central power and the increased importance of non-Romans resulted in internal Roman factors. Migrations, and the use of non-Romans in the military, were known in the periods before and after, and the Eastern Roman Empire adapted and continued to exist until the fall of Constantinople to the Ottomans in 1453. The fall of the Western Roman Empire, although it involved the establishment of competing barbarian kingdoms, was to some extent managed by the eastern emperors.

The migrants comprised war bands or tribes of 10,000 to 20,000 people, but in the course of 100 years they numbered not more than 750,000 in total, compared to an average 40 million population of the Roman Empire at that time. Although immigration was common throughout the time of the Roman Empire, the period in question was, in the 19th century, often defined as running from about the 5th to 8th centuries. The first migrations of peoples were made by Germanic tribes such as the Goths (including the Visigoths and the Ostrogoths), the Vandals, the Anglo-Saxons, the Lombards, the Suebi, the Frisii, the Jutes, the Burgundians, the Alemanni, the Sciri and the Franks; they were later pushed westward by the Huns, the Avars, the Slavs and the Bulgars. Later invasions, such as the Vikings, the Normans, the Varangians, the Hungarians, the Moors, the Romani, the Turkics, and the Mongols also had significant effects (especially in North Africa, the Iberian Peninsula, Anatolia and Central and Eastern Europe).