While backend integration is well understood, structured knowledge on frontend integration remains limited. Modern web applications increasingly require late-bound integration at the UI level to enable independent evolution, reduce deployment dependencies, and support modular architectures. Unlike backend integration, frontend integration allows composing user-facing components without prior coordination on data structures or API contracts. This paper defines key concepts such as backend runtime, frontend runtime, and web infrastructure before introducing a taxonomy of six frontend integration patterns: Navigate with Hyperlinks, Embed in Isolated Frames, Transclude Content, Compose with Self-Contained Components, Plug-in Modules, and Preserve Return URIs. By documenting these patterns, we provide a structured approach to designing scalable, maintainable, and loosely coupled frontend architectures.