When historians refer to "The Black Death," they mean the specific outbreak of plague that took place in Europe in the mid-14th century. The Black Death came to Europe in October of 1347, spread swiftly through most of Europe by the end of 1349 and on to Scandinavia and Russia in the 1350s. It returned several times throughout the rest of the century.

The Black Death was also known as The Black Plague, the Great Mortality, and the Pestilence.

Traditionally, the disease that most scholars believe struck Europe was "Plague." Best known as bubonic plague for the "buboes" (lumps) that formed on the victims' bodies, Plague also took pneumonic and septicemic forms. Other diseases have been postulated by scientists, and some scholars believe that there was a pandemic of several diseases; but currently the theory of Plague (in all its varieties) still holds among most historians.

To date no one has been able to identify the point of origin of the Black Death with any precision. It started somewhere in Asia, possibly in China, possibly at Lake Issyk-Kul in central Asia.

Bubonic Plague was spread by the fleas who lived on plague-infected rats, and such rats were ubiquitous on trading ships.
Pneumonic Plague could spread with a sneeze and jump from person to person with terrifying speed.
Septicemic Plague spread through contact with open sores.
Through these methods of contagion, the Black Death spread via trade routes from Asia to Italy, and thence throughout Europe.

It is estimated that approximately 20 million people died in Europe from the Black Death. This is about one-third of the population. Many cities lost more than 40% of their residents, Paris lost half, and Venice, Hamburg and Bremen are estimated to have lost at least 60% of their populations.

Medieval people believed that God was punishing mankind for its sins. There were also those who believed in demonic dogs, and in Scandinavia, the superstition of the Pest Maiden was popular. Some people accused the Jews of poisoning wells; the result was a horrific persecution of Jews that the papacy was hard-put to stop. Scholars attempted a more scientific view, but they were hampered by the fact that the microscope wouldn't be invented for several centuries. The University of Paris conducted a study, the Paris Consilium, which, after serious investigation, ascribed the plague to a combination of earthquakes and astrological forces.