Apollo Client simplifies GraphQL integration in frontend applications. Install @apollo/client and graphql packages. ApolloClient configuration includes URI and cache settings. InMemoryCache caches query results for offline support. useQuery hook fetches data declaratively with loading states. useMutation hook sends data modifications. useSubscription hook manages real-time data streams. request specific fields with nested structure. Mutations modify data with defined return types. Subscriptions provide real-time updates through WebSocket connections. Fragments reuse field selections across queries. Optimistic updates show changes before server confirmation. Pagination with relay-style cursor connections. Error policies control error handling behavior. Local state management with @client and reactive variables. Apollo Studio for schema exploration and debugging. Apollo Link chain customizes request processing. TypeScript integration provides type safety for GraphQL operations. Apollo Cache persists across sessions with apollo3-cache-persist. Apollo Client is the standard GraphQL client for React applications.