Along with the maturing of blockchain technology, the scope of Web3 has been expanding from hash rate to crypto market, then from crypto market to metaverse. This book introduces the origin of the Web3 concept, before looking into the infrastructure of Web3, namely the blockchain and its main applications -- the development of which started from the genesis block of BTC to date. The book also covers the key developing tracks of the current Web3 world, including DeFi, NFT, GameFi, DAO and Metaverse. A review of the 'twins' of Web3 -- investors and regulators -- in the regulation of this field wraps up the discussion.