The series is set 97 years after a devastating nuclear war wiped out almost all life on Earth. The only survivors are the residents of twelve space stations in Earth's orbit prior to the war, and the descendants of the people on earth who survived the war, called "grounders" by the 100. The space stations banded together to form a single massive station named "The Ark", where about 2,400 people live. Resources are scarce and all crimes no matter their nature or severity are punishable by death ("floating") unless the perpetrator is under 18 years of age. After the Ark's life support systems are found to be critically failing, one hundred juvenile prisoners are declared "expendable" and sent to the surface in a last ditch attempt to determine if Earth is habitable again.

The series premiere was watched by an estimated 2.7 million American viewers, and received an 18-49 rating of 0.9. It is considered the most-watched show in its time-slot on The CW since 2010 with the series Life Unexpected.

71% score on Rotten Tomatoes: Although flooded with stereotypes, the suspenseful atmosphere helps make The 100 a rare high-concept guilty pleasure.