# Building AR Experiences with RealityKit

RealityKit is Apple's primary rendering, animation, physics, and audio engine built from the ground up for AR. When combined with ARKit's world-tracking capabilities, it provides a powerful foundation for immersive applications.

Component-Based Entity System

The core of RealityKit is its Entity-Component-System (ECS). Unlike UIKit or traditional scene graphs, ECS favors composition over inheritance.

You create an `Entity`, and attach components like `ModelComponent`, `CollisionComponent`, or custom components to give it properties and behavior.

Working with Anchors

To place objects in the real world, you use `AnchorEntity`. These can be attached to planes, images, body parts, or specific points in space.

Performance Considerations

When building complex AR scenes, polygon count and texture resolution matter. Always optimize your USDZ files before bringing them into Reality Composer or Xcode. Use RealityKit's built-in physics engine sparingly for a large number of dynamic objects, as calculations can drain battery quickly.