Two lives met across death and centuries. To ask what it meant is meaningless. There is no destiny. But sometimes there is bravery

Colonization means potential immortality for the human genus. Man's safety on Earth was never great, and it dwindles hourly. Disarmament, even world government, will not guarantee survival in an age when population presses natural resources to the limit and when the knowledge of how to work mischief on a planetary scale is ever more widely diffused among peoples who may grow ever more desperate.

What five books would I like to be remembered for? Well... Tau Zero, I like that one especially. It was somewhat of a tour de force, and I think it got across what I was trying for.

A fanatic's willingness to kill or be killed in the service of a cause cannot prove the rightness of that cause.

My knowledge of the human psyche is as yet imperfect. Certain areas won't yield to computation.

I have yet to see any problem, however complicated, which, when you looked at it in the right way, did not become still more complicated.

If we knew exactly what to expect throughout the Solar System, we would have no reason to explore it.