Auto Layout is a constraint-based layout system that automatically calculates the size and position of views based on rules (constraints) you define. It's important because:

• Responsive Design: Adapts to different screen sizes and orientations
• Dynamic Content: Handles varying content sizes automatically
• Internationalization: Supports different languages and text directions
• Accessibility: Works with Dynamic Type and accessibility features

Auto Layout uses mathematical relationships between views instead of fixed frames, making UIs flexible and maintainable.