This paper presents stretchable, transparent, ionic conductors (STICs) that enable the fabrication of devices with new attributes. STICs achieve high-voltage and high-frequency electromechanical transduction without electrochemical reactions. They exhibit 99.99% transmittance at 550 nm, linear strain beyond 500%, and sheet resistance below 200 Ω/sq. These conductors have lower electrical resistance than existing stretchable and transparent electronic conductors at large stretch and high transmittance. STICs offer new opportunities for scientific exploration and applications. The paper demonstrates that ionic conductors can be used to fabricate devices operating at high voltage and high frequency. An actuator achieving large deformation at high voltage and a loudspeaker producing sound across the entire audible range are presented. These devices are essentially perfectly transparent to light across the entire visible range. The fundamental limits of electromechanical transduction are studied through experiments and theory. The strain of actuation is not limited by the elasticity of the soft ionic conductors, but by electromechanical instability. The frequency of actuation is not limited by electrical resistance, but by mechanical inertia. The paper describes a basic design of stretchable ionics, which places two electrodes, an electrolyte, and a dielectric in series. The electrode/electrolyte interface forms an electrical double layer. For certain combinations of electrode and electrolyte, if the voltage across the interface is within a certain range, the interface is ideally polarizable, and the electrical double layer behaves like a capacitor. The electrolyte and dielectric in series establish capacitive coupling between the electrical signals carried by the two electrodes, and transport power with alternating current. The paper demonstrates the remarkable properties of STICs by building a transparent, high-speed, large-strain actuator using a design called a "layered electrolytic and dielectric elastomer" (LEADER). A membrane of a dielectric elastomer is sandwiched between two membranes of the electrolytic elastomer. The electrolytes and the dielectric are stretchable and transparent, but the electrodes need not be. When a voltage is applied between the electrodes, ions of different charge polarities collect on the two electrolyte/dielectric interfaces, causing the sandwich to reduce its thickness and enlarge its area. The paper also demonstrates a transparent loudspeaker that produces sound from 20 Hz to 20 kHz. The loudspeaker is placed in front of a laptop, which plays music videos. The screen of the laptop is clearly visible through the loudspeaker. The sound tracks of the videos are fed to the loudspeaker as analog voltage signals, from the audio output of the laptop, through a high-voltage amplifier. The paper shows that the frequency of actuation is not limited by electrical resistance, but by mechanical inertia. The time to charge the device, the RC delay, scales as τRC ∼ cThis paper presents stretchable, transparent, ionic conductors (STICs) that enable the fabrication of devices with new attributes. STICs achieve high-voltage and high-frequency electromechanical transduction without electrochemical reactions. They exhibit 99.99% transmittance at 550 nm, linear strain beyond 500%, and sheet resistance below 200 Ω/sq. These conductors have lower electrical resistance than existing stretchable and transparent electronic conductors at large stretch and high transmittance. STICs offer new opportunities for scientific exploration and applications. The paper demonstrates that ionic conductors can be used to fabricate devices operating at high voltage and high frequency. An actuator achieving large deformation at high voltage and a loudspeaker producing sound across the entire audible range are presented. These devices are essentially perfectly transparent to light across the entire visible range. The fundamental limits of electromechanical transduction are studied through experiments and theory. The strain of actuation is not limited by the elasticity of the soft ionic conductors, but by electromechanical instability. The frequency of actuation is not limited by electrical resistance, but by mechanical inertia. The paper describes a basic design of stretchable ionics, which places two electrodes, an electrolyte, and a dielectric in series. The electrode/electrolyte interface forms an electrical double layer. For certain combinations of electrode and electrolyte, if the voltage across the interface is within a certain range, the interface is ideally polarizable, and the electrical double layer behaves like a capacitor. The electrolyte and dielectric in series establish capacitive coupling between the electrical signals carried by the two electrodes, and transport power with alternating current. The paper demonstrates the remarkable properties of STICs by building a transparent, high-speed, large-strain actuator using a design called a "layered electrolytic and dielectric elastomer" (LEADER). A membrane of a dielectric elastomer is sandwiched between two membranes of the electrolytic elastomer. The electrolytes and the dielectric are stretchable and transparent, but the electrodes need not be. When a voltage is applied between the electrodes, ions of different charge polarities collect on the two electrolyte/dielectric interfaces, causing the sandwich to reduce its thickness and enlarge its area. The paper also demonstrates a transparent loudspeaker that produces sound from 20 Hz to 20 kHz. The loudspeaker is placed in front of a laptop, which plays music videos. The screen of the laptop is clearly visible through the loudspeaker. The sound tracks of the videos are fed to the loudspeaker as analog voltage signals, from the audio output of the laptop, through a high-voltage amplifier. The paper shows that the frequency of actuation is not limited by electrical resistance, but by mechanical inertia. The time to charge the device, the RC delay, scales as τRC ∼ c