Electrochromism (EC) is a unique property of certain materials that undergo an electrochemical-induced change in colouration. During the last decades, electrochromic materials (ECMs) have been applied in a variety of technologies ranging from smart windows to information displays and energy storage devices. More recently, ECMs have attracted the attention of the (bio)sensing community thanks to their ability to combine the sensitivity of electrochemical methods with the intuitive readout of optical sensors. Although still a nascent technology, EC-based sensors are on the rise with several targets (e.g. cancer biomarkers, bacteria, metabolites and pesticides), which have already been detected by (bio)sensors using ECMs as transducers. In this review, we provide the reader with all the information to understand EC and its use in the development of EC-based biosensors.