GraphQL Joins` is a feature released by Hasura v2.6.0 that enables federating queries and mutations across multiple GraphQL services as if they were a single GraphQL schema without modifying any of the underlying APIs or writing extra code. This allows for unified data access and querying across independent GraphQL services, REST APIs, and databases. With `GraphQL Joins`, developers can create relationships between entities in different schemas, unify their GraphQL API, and improve performance by caching frequently executed queries. The feature also supports authentication, authorization, and schema evolution management, making it a powerful tool for building scalable and maintainable GraphQL applications.