The Original Series Premise              

"Theorizing that one could time-travel within his own lifetime, Dr. Sam Beckett led an elite group of scientists into the desert to develop a top secret project known as Quantum Leap.

He awoke to find himself trapped in the past, facing mirror images that were not his own, and driven by an unknown force to change history for the better.

His only guide on this journey is Al, an observer from his own time, who appears in the form of a hologram that only Sam can see and hear.

Trapped in the past, Dr. Beckett finds himself leaping from life to life, striving to put right what once went wrong and hoping each time that his next leap will be the leap home."

The Revival Series Premise

"Dr. Ben Song risked everything when he used the
Quantum Leap accelerator to travel back in time. 
As he Leaps between bodies with no memory
of who he is, he still has one hope:
That his next Leap takes him back
to the place and people he calls home."