The result is a unified concurrency model providing both thread abstractions and event abstractions. We implemented the unified concurrency model in Haskell Our implementation demonstrates how to use these techniques by building an application-level thread library with support for multiprocessing and asynchronous I/O mechanisms in Linux. The thread library is type-safe, is relatively simple to implement, and has good performance. Application-level threads are extremely lightweight (scaling to 10,000,000 threads!) and our scheduler, which is implemented as a modular and extensible event-driven system, outperforms NPTL in I/O benchmarks.