IntroductionModified electrodes functionalized with various organic monolayers and thin films attached to their conducting surfaces have found numerous applications in electrocatalysis, sensors, and fuel cells [1][2][3][4][5][6][7]. Particularly, active research was directed to the applications of modified electrodes in different bioelectrochemical systems [8,9], including biosensors [10-13] and biofuel cells [14][15][16][17]. In the past decade, different modified electrodes functionalized with signal-responsive molecules [18], polymers [19], or supramolecular complexes [20] were developed to ''switch on demand'' electrochemical properties of electrode surfaces. Their applications in switchable biosensors [21], fuel cells [22], and electrochemical systems processing information [23] have been suggested. Various physical and/or chemical signals as well as their combinations were used to switch electrochemical properties of the modified interfaces between active and inactive states for specific electrochemical, electrocatalytic, and bioelectrocatalytic reactions. Light signals (irradiation of electrodes with visible or ultraviolet light) [24-31], magnetic field applied at electrode surfaces loaded with magnetic particles or magnetic nanowires [32][33][34][35][36][37][38][39][40][41][42][43], and electrical potentials producing chemical changes at the electrode surfaces [44][45][46][47][48] were used to reversibly alternate electrochemical properties of the modified electrodes. Chemical [29,[49][50][51] or biochemical [52] signals resulting in reversible changes of the interfacial properties were also used to switch the electrode activity ON/OFF for specific electrochemical transformations. The present chapter gives an overview of different signal-responsive electrochemical interfaces, emphasizing the importance of scaling up the complexity of the signal-processing systems and their applications in unconventional information-processing systems.