This chapter discusses paper-based (PB) electrochemical sensors. The fundamentals of operation of electrochemical sensors are reviewed. The advantages of paper for developing such devices are analyzed, and the preferred paper types for these purposes are shown. Possible configurations of electrochemical sensors and technological approaches used for their fabrication are discussed. The main attention is paid to the fabrication of electrodes, the formation of hydrophobic barriers and the modification of electrodes. and the fundamentals of their design, operation, performance, and application are discussed. It is shown that all modes developed for traditional sensors can be used in the operation of paper electrochemical sensors. The chapter concludes with an analysis of future trends in the development of PB electrochemical sensors.