  Coronal mass ejections (CMEs) are relatively a recently-discovered
phenomenon, in 1971, some fifteen years into the Space Era. It took another two
decades to realize that CMEs are the most important players in solar
terrestrial relationship as the root cause of severe weather in Earth's space
environment. CMEs are now counted among the major natural hazards because they
cause large solar energetic particle (SEP) events and major geomagnetic storms,
both of which pose danger to humans and their technology in space and ground.
Geomagnetic storms discovered in the 1700s, solar flares discovered in the
1800s, and SEP events discovered in the1900s are all now found to be closely
related to CMEs via various physical processes occurring at various locations
in and around CMEs, when they interact with the ambient medium. This article
identifies a number of key developments that preceded the discovery of
white-light CMEs suggesting that CMEs were waiting to be discovered. The last
two decades witnessed an explosion of CME research following the launch of the
Solar and Heliospheric Observatory mission in 1995, resulting in the
establishment of a full picture of CMEs.
