It is not easy to see how the more extreme forms of nationalism can long survive when men have seen the Earth in its true perspective as a single small globe against the stars.

When you finally understand the universe, it will not only be stranger than you imagine, it will be stranger than you can imagine.

Isn't killing people in the name of God a pretty good definition of insanity?

Many, and some of the most pressing, of our terrestrial problems can be solved only by going into space. Long before it was a vanishing commodity, the wilderness as the preservation of the world was proclaimed by Thoreau. In the new wilderness of the Solar System may lie the future preservation of mankind.

I have never grown up, but I will never stop growing.

Open the pod bay doors, Hal.

The numbers of distinct human societies or nations, when our race is twice its present age, may be far greater than the total number of all the men who have ever lived up to the present time.