Three.js is an open-source JavaScript library that makes browser-based 3D rendering approachable by wrapping WebGL behind a scene graph of geometries, materials, lights, cameras and renderers, with loaders for common model formats and helpers for animation and object picking.
The site provides a getting-started guide, a searchable API reference, a large collection of live examples with viewable source code, and documentation for addons such as orbit controls, post-processing, physics integrations and glTF asset loading.
It suits front-end developers building product configurators, data visualisations, interactive maps, educational simulations and lightweight browser games, as well as designers prototyping interactive scenes without adopting a dedicated game engine.
Compared with raw WebGL it removes a great deal of boilerplate; compared with full game engines it leaves physics, asset pipelines and editor tooling to other libraries, which keeps bundles smaller but requires more assembly work.
Check WebGL support and device performance before promising complex scenes, dispose geometries and textures when unmounting views to avoid memory leaks, and pin the library version because addon import paths have changed across releases.