A rapidly emerging and increasingly applied technology, ultracapacitors are capable of storing and discharging energy very quickly and effectively. Due to their many benefits, ultracapacitors are currently being utilized in thousands of different applications, and considered in an equally diverse range of future applications. Ultracapacitors complement a primary energy source which cannot repeatedly provide quick bursts of power, such as an internal combustion engine, fuel cell or battery. The future horizon looks brilliant for ultracapacitors, which already rank as a powerful alternative energy resource.