  Blockchain enables a digital society where people can contribute,
collaborate, and transact without having to second-guess trust and
transparency. It is the technology behind the success of Bitcoin, Ethereum, and
many disruptive applications and platforms that have positive impact in
numerous sectors, including finance, education, health care, environment,
transportation, and philanthropy, to name a few. This chapter provides a
friendly description of essential concepts, mathematics, and algorithms that
lay the foundation for blockchain technology.
