What is Scala's approach to concurrency with Futures and Promises?

Scala's concurrency model separates Future (read-only, result of async computation) from Promise (writable, fulfills a Future). Promise creates a Future and completes it manually: val p = Promise[Int](); val f = p.future; p.success(42) // or p.failure(exception). This is useful when wrapping callback-based APIs. ExecutionContext: defines where Future code runs. ExecutionContext.global uses a fork-join pool sized to available CPUs. Custom: ExecutionContext.fromExecutorService(Executors.newFixedThreadPool(8)). Combining Futures: Future.sequence runs in parallel and collects results. Future.traverse maps then sequences. zip: combine two futures. recover: handle failures. Blocking: Await.result(future, 5.seconds) blocks the calling thread — avoid in production async code. For purely functional async, consider Cats Effect IO or ZIO as more powerful alternatives.