Beam is a cryptocurrency developed based on the MimbleWimble protocol, with strong privacy, substitutability and scalability. All Beam transactions are private by default. New nodes joining the network do not need to synchronize the entire transaction history, but can request to synchronize only the compressed history and block headers of the system state to achieve fast synchronization. Beam is a new coin that attempts to implement MimbleWimble, written from scratch in C++. Compared with Grin, the total amount of tokens of Grin is unlimited, while the Beam token has a limited supply and periodic rewards are halved.