The popularity of cryptocurrencies such as Bitcoin and the underlying blockchain technology presents both challenges and opportunities to the energy sector. As interest in Bitcoin and other cryptocurrencies has increased, the energy demand to support cryptocurrency "mining" activities has also increased. The increased energy demand-when localized-can exceed the available power capacity and increase customers' electricity rates. On the other hand, not all cryptocurrencies require energy-intensive mining operations. In addition, blockchain technologies could present opportunities for the energy sector by facilitating energy and financial transactions on a smart grid. Bitcoin and other cryptocurrencies can be used to make payments without banks or other third-party intermediaries, and are sometimes considered virtual currency. The technology underlying these cryptocurrencies is blockchain. A blockchain is a digital distributed ledger that enables parties who may not otherwise trust one another to agree on the current ownership and distribution of assets in order to conduct new business. New blocks may be added to a blockchain through a variety of methods. In mining blocks, users seek to add the next block to the chain. For Bitcoin, new blocks are added to the blockchain through a proof-of-work (PoW) algorithm. Under PoW, miners-those seeking to add a block to a blockchain-are presented a difficult computational problem. Once the problem is solved, other users can validate the solution and confirm the block, adding the next block to the chain. In the case of Bitcoin, miners who create and publish new blocks are rewarded with Bitcoin. Less energy intensive, alternative algorithms exist, such as proof of stake and proof of authority. Cryptocurrency mining through PoW requires substantial energy to operate and thermally regulate the requisite hardware. Devices have different performance capabilities and have different power requirements. Generally, the device, or a cluster of devices, that can perform more calculations per second will require more energy for powering and cooling. Global power requirement estimates for Bitcoin have increased within the last five years. Network power estimates for 2018 range between 2,500 megawatts (MW) and 7,670 MW, which is nearly 1% of U.S. electricity generating capacity. Opinions differ on whether future growth in Bitcoin will significantly impact energy consumption and subsequent carbon dioxide (CO2) emissions. Cryptocurrency mining includes costs associated with equipment, facilities, labor, and electricity. Some users pool computational resources to solve PoW problems faster, and are on a worldwide hunt for cheap, reliable electricity. While many mining pools are in China, some have been able to utilize closed industrial facilities in the United States that can provide affordable abundant electricity. A 2017 study found that nearly three-quarters of all major mining pools are based in either China (58%) or in the United States (16%). Governments are developing various policies in response to growth in energy demand by cryptocurrency mining activities. In some areas, applications from potential mining companies have exceeded the available capacity. Other areas have offered reduced electricity rates to attract miners. In the United States, federal policy options to improve energy efficiency of mining operations include minimum energy conservation standards and data center energy efficiency standards. In addition to the challenges that cryptocurrency mining presents to the energy sector, there are also opportunities, particularly for blockchain. These may include electric vehicle charging infrastructure and distributed energy resources, among others. The U.S. electricity grid is critical infrastructure and subject to regulation. Opinions differ as to a potential role for blockchain technology in the energy sector.