Asynchronous circuits are digital circuits that operate without a global clock signal. Instead of relying on a clock to synchronize operations, these circuits use handshaking signals to communicate between components. This allows for more flexible timing and can lead to lower power consumption and increased speed, as components can work independently. In contrast to synchronous circuits, which can suffer from clock skew and timing issues, asynchronous circuits can be more efficient in certain applications. They are often used in low-power devices, high-speed processors, and communication systems where timing precision is crucial and power efficiency is desired.