This article explores the measurement of electric current using optical fibers, primarily through the Faraday effect, also known as the magneto-optic effect. Fiber-Optic Current Sensors (FOCS) offer high accuracy, modularity, and easy installation. Now available for uni- or bi-directional dc current measurement up to 500kA, with corresponding sensor head sizes, it offers an easily installed, interference-free alternative to the Hall. Accurate measurement of electrical current in devices is a fundamental technology that is essential for controlling and monitoring the systems and equipment that many industries and our daily lives depend upon.