No trilogy should have more than four books.

The best proof of intelligent life in space is that it hasn't come here.

Only small minds are impressed by large numbers.

He was moving through a new order of creation, of which few men had ever dreamed. Beyond the realms of sea and land and air and space lay the realms of fire, which he alone had been privileged to glimpse. It was too much to expect that he would also understand.

Some things have eternal value, and compassion is one of them. I hope we never lose that. Compassion for humans as well as animals.

It will be possible in a few more years to build radio controlled rockets which can be steered into such orbits beyond the limits of the atmosphere and left to broadcast scientific information back to the Earth. A little later, manned rockets will be able to make similar flights with sufficient excess power to break the orbit and return to Earth. (1945) [Predicting communications satellites.]

Humor was the enemy of desire.