A brand identity is the visual language of the company — logo, colour, typography, and the principles that govern how they're used across all external communications. A design system is the component library and interaction patterns used to build the product UI — buttons, form elements, spacing tokens, and the coded assets the engineering team uses. They should be coherent with each other, built from the same visual principles, but they serve different purposes and are built by different disciplines. A brand identity agency builds the identity; a product design team builds the design system that inherits from it.
