Space Exploration & Colonization involves humans or human-built machines traveling to other planets, star systems, or galaxies.
Possible motivations include curiosity, reducing the chance of existential risks, and expanding human civilization.
Possible techniques include both present or near-future technology and speculative future technology.
For the question of why alien civilizations haven't space-colonized us, see Great Filter.
Related Sequences: So You Want To Colonize The Universe