222 books • 51 series
Aliens Among Us: The Evidence (Set) (21st Century Skills Library: Aliens Among Us: The Evidence)
Extraterrestrial: Past, Present, and Future (21st Century Skills Library: Aliens Among Us: The Evidence)
Area 51 and Other Top Secret Science (21st Century Skills Library: Aliens Among Us: The Evidence)
Finding Life in the Universe (21st Century Skills Library: Aliens Among Us: The Evidence)