There have been three great pandemics of bubonic plague in history:

The first was Justinian's Plague that began in 542 and lasted until 662.

The second was the Black Death that began in 1347 and lasted until 1665. 38-39 million people died between 1347-1351.

The third began in Yunnan, China in 1892 and spread to India by 1896, killing approximately 6 million people in India alone.

Bubonic plague is the most common, and, without antibiotics, is fatal 50-60% of the time.

Pneumonic plague is less common, is extremely contagious, and is fatal 95% of the time.

Septicaemic plague, which is fortunately very rare, attacks the bloodstream and is always fatal.