The Three Laws of Robotics

1. A robot may not injure a human being, or, through inaction, allow a human being to come to harm.
2. A robot must obey the orders given it by human beings except where such orders would conflict with the First Law.
3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law.

From Handbook of Robotics, 56th Edition, 2058 A.D., as quoted in I, Robot.
In Robots and Empire (ch. 63), the "Zeroth Law" is extrapolated, and the other Three Laws modified accordingly:

0-th. A robot may not injure humanity or, through inaction, allow humanity to come to harm.

Unlike the Three Laws, however, the Zeroth Law is not a fundamental part of positronic robotic engineering, is not part of all positronic robots, and, in fact, requires a very sophisticated robot to even accept it.

Asimov claimed that the Three Laws were originated by John W. Campbell in a conversation they had on December 23, 1940. Campbell in turn maintained that he picked them out of Asimov's stories and discussions, and that his role was merely to state them explicitly