Bitcoin and Blockchain; challenges, opportunities, and applications in smart city and transportation Abstract Cryptocurrencies championed by Bitcoin have emerged as a subject for intense debate. However, it is their underlying technology, the Blockchain, that has intrigued many given its promising applications in smart cities and transportation. In this article, we first elaborate on the Bitcoin, the Blockchain and the concept of the Ethereum ‘s “smart contract”. We the survey potential applications of the Blockchain in transportation, logistics, and supply chains, as well as insurance, health, education, finance, real estate, land administration, energy, social networks, tax policy, etc. The paper can be used by a broader range of readers who want to understand the basic principle of cryptocurrencies and Blockchain as well as their challenges and advantages. Keywords: Bitcoin; Blockchain; Ethereum; Smart Contract; Smart Cities; Transportation 1