The Green Hills of Earth. Menace from Earth: Robert Heinlein

First Time in Mass Market for These Two Perennially Top-Selling Heinlein Books in a Single Volume.
"Not only 's premier writer of speculative fiction, but the greatest writer of such fiction in the world." -Stephen King
Two of the Grand Master's finest:
The saga of the opening of the space frontier as courageous men and women risked their lives to build the first space station and colonize the Moon and Venus, while praying for one last landing on the globe that gave them birth, to return to The Green Hills of Earth.
From a mysterious region on Earth, where a more advanced lifeform may be studying the interesting creatures called "humans," to the first moon colony, where a young girl's relationship with her boyfriend is endangered by the beautiful Menace from Earth.