This document summarizes a talk on blockchain technology for developers. It discusses key concepts like digital signatures, cryptographic hash functions, Merkle trees, distributed consensus, and different failure models. It then covers the use of blockchains for applications like e-cash and titles. Specific blockchain protocols like Bitcoin and Ethereum are examined, looking at transactions, scripting, and addressing schemes. Scalability, off-chain solutions, and alternative consensus mechanisms are also addressed. The talk concludes with advice around building on existing frameworks rather than designing one's own crypto or blockchain from scratch.