This document provides an overview of world-building for fiction writing. It discusses three main categories of world-building: 1) Imaginary worlds, which are entirely fictional universes found in fantasy genres. 2) Alternate reality, which are re-imaginings of our existing world popular in sci-fi. 3) Actual locations, using real places without fantasy elements. It then focuses on imaginary worlds, providing examples from Tolkien and giving tips on deciding starting points, asking questions about the world, and drawing inspiration from real history and locations. It also discusses blending fantasy with our world, as in Harry Potter. Finally, it covers alternate reality world-building in sci-fi and its use of the "what