Blockchain builds a trustworthy service among parties that do not have to trust each other. In recent years, blockchain applications have exploded, ranging from financial services to governmental applications. In this article, we review blockchain consensus, the crucial building block for blockchains to achieve security goals. By selectively discussing the trade-offs made by each type of consensus protocol and conducting a review of blockchain-related standards, we discuss why we need to standardize blockchain consensus and what challenges are yet to be solved before or even after blockchain consensus is standardized.