Booking Token Unit (BTU) protocol is a standardized building block for any decentralized application (dApp) or web site willing to implement booking features for their end-users. The BTU protocol also brings interoperability among decentralized applications that incorporate it. BTU protocol is currently under standardization in the Ethereum ecosystem as ERC-808. BTU token will be an ERC20 token running the protocol. All platforms implementing the BTU protocol would benefit from a hybrid approach combining an on-chain smart contract and off-chain software components, providing more scalability. A transparent and public inventory enabled by an open-source protocol would considerably lower the entry barriers to many internet booking markets.