The Arbitrum blockchain protocol started as a Princeton University research project, and has grown into a robust community hosting hundred of applications and over 600,000 monthly users. Along the way, the system has evolved through at least three generations to meet the needs of developers and users. This talk will provide a technical description of how Arbitrum works, as an example of a modern blockchain protocol, along with a perspective on the history and future of blockchain technology. Ed Felten is the co-founder and chief scientist at Offchain Labs, Inc. He is the Robert E. Kahn Professor Emeritus of Computer Science and Public Affairs and the Founding Director of the Center for Information Technology Policy.