The ThreadLocal class appeared with little fanfare in version 1.2 of the Java platform. While support for thread-local variables has long been a part of many threading facilities, such as the Posix pthreads facility, the initial design of the Java Threads API lacked this useful feature. Further, the initial implementation was quite inefficient. For these reasons, ThreadLocal gets relatively little attention, but it can be very handy for simplifying the development of thread-safe concurrent programs. This article examines ThreadLocal and offers tips for exploiting its power.