Abstract: Asynchronous networks-on-chip(NoCs) are promising candidates for future multi-core chip-multiprocessors and systems-on-chip due to their low dynamic energy dissipation,tolerance to delay variations,unified network interfaces,easy system integration and excellent electro-magnetic compatibility.After a small introduction of asynchronous circuits,the current research progress of asynchronous NoCs have been reviewed from different aspects including topologies,async/sync interfaces,flow control methods,quality-of-service,routing algorithms,low power design,fault-tolerance and testing,and design automation.A case study of several representative designs of asynchronous NoCs is provided.It is shown that asynchronous NoCs have many advantages over their synchronous counterparts and a significant portion of future many-core systems will use asynchronous NoCs as their on-chip communication structures,but it is urgent to improve their usability and network performance.