Today, ion-selective electrodes are among the most versatile and attractive tools in analytical chemistry because they enable direct, rapid and low-cost measurements using relatively simple instrumentation. Their response is based on the establishment of a phase-boundary potential at the electrode membrane/sample interface that depends on the activity (concentration) of the analyte in the sample according to the Nernst equation. Conveniently, the electrode response can be readily tailored to a given analytical task by optimizing the membrane composition. The overall versatility of ion-selective electrodes and their compatibility with a wide range of analytes and sample types contributed to their widespread adoption in clinical and environmental analysis. More recently, they accelerated the development of new technologies, such as wearable sensors, point-of-care devices and sensing platforms for in-situ environmental monitoring. The potential of an ion-selective electrode in a sample is measured against a reference electrode, which is designed to maintain a constant potential independent of the composition of the analyzed medium. Double junction reference electrodes, based on an Ag/AgCl element immersed into an internal filling solution and connected to the sample via an aqueous bridge electrolyte, have established themselves as robust and reliable tools in potentiometric analysis over the past century. However, recent advances in wearable and deployable sensing systems have created a demand for novel reference electrodes that combine good analytical performance with simplified integration into miniaturized platforms.