Books about Human-alien encounters -- Fiction (sorted alphabetically)
- Learning Theory James V. McConnell
- Leave, Earthmen—Or Die! John Massie Davis
- Left hand, right hand James H. Schmitz
- Lesson for Today Joel Nydahl
- License to Steal Louis Newman
- Lights on Precipice Peak Stephen Tall
- Little Fuzzy H. Beam Piper
- Little Knowledge R. R. Winterbotham
- Little men of space Frank Belknap Long
- Little Monsters Come Ray Cummings
- Little Pets of Arkkhan Bill Garson
- Lonely Ones Edward W. Ludwig
- Lord of a Thousand Suns Poul Anderson
- Lorelei Charles V. De Vet
- Lumen Camille Flammarion
- Lunarian Professor and His Remarkable Revelations Concerning the Earth, the Moon and Mars James B. Alexander
- Lunar Station Harl Vincent
- Madcap Metalloids Verne Athanas
- Madman From Earth Keith Laumer
- Madmen of Mars Erik Fennel
- Man From Siykul Richard Wilson
- Manners and Customs of the Thrid Murray Leinster
- man who liked lions John Bernard Daley
- Margenes Miriam Allen De Ford
- Martian Allen Glasser and A. R. Hilliard