Bring an array of aliens--both weird and familiar--to your science fantasy adventures with Interstellar Species, the newest rulebook for the Starfinder Roleplaying Game! This gorgeously illustrated reference provides deep dives on 25 playable Starfinder species, each with thematic player options usable by any character, plus new options for 7 Starfinder character classes. There's also a system for easily creating your own playable species, and a catalog of around 100 thematic nonplayer characters ready to slot into any adventure! A new class, the evolutionist, allows you to transform yourself over time into an eldritch being, mechanized construct, sepulchral undead, or riot of biological potential, each with unique abilities--and drawbacks, should you allow your transformation to grow out of control.