Design tokens are the foundational building blocks of every modern design system. They represent the smallest decisions — colors, spacing, typography, shadows — as named, reusable values that flow from design tools to code without manual translation. When implemented correctly, tokens create a single source of truth that scales across platforms and teams.

The challenge lies in governance. As token libraries grow, teams face difficult questions about naming conventions, versioning strategies, and the boundary between global tokens and component-specific overrides. The most successful systems we've studied adopt a three-tier architecture: primitive, semantic, and component tokens.

Primitive tokens define the raw palette — every shade, every spacing step, every font weight. Semantic tokens map meaning onto primitives: "color-action-primary" points to a specific blue. Component tokens scope decisions to individual patterns. This layering keeps the system flexible without sacrificing consistency, but requires disciplined governance and clear documentation.