Rigid electromagnetic actuators serve our society in a myriad of ways for more than 200 years. However, their bulky nature restricts close collaboration with humans. Here, we introduce soft electromagnetic actuators (SEMAs) by replacing solid metal coils with liquid-metal channels embedded in elastomeric shells. We demonstrate human-friendly, simple, stretchable, fast, durable, and programmable centimeter-scale SEMAs that drive a soft shark, interact with everyday objects, or rapidly mix a dye with water. A multicoil flower SEMA with individually controlled petals blooms or closes within tens of milliseconds, and a cubic SEMA performs programmed, arbitrary motion sequences. We develop a numerical model supporting design and opening potential routes toward miniaturization, reduction of power consumption, and increase in mechanical efficiency. SEMAs are electrically controlled shape-morphing systems that are potentially empowering future applications from soft grippers to minimally invasive medicine.

Realizing a sustainable, technologically advanced future will necessitate solving the electronic waste problem. Biodegradable forms of electronics offer a viable path through their environmental benignity. With both the sheer number of devices produced every day as well as their areas of application ever increasing, new concepts of degradable batteries able to sustain the high power demands of modern electronics must be developed. Simultaneously, integration of electronics in close interaction with its user or powering soft robotic devices necessitates high degrees of compliance, rendering stretchable batteries indispensable. Here, a concept for merging intrinsically stretchable materials with engineered stretchability by kirigami‐patterning on a component level is shown to yield high‐power biodegradable batteries with reversible elasticity up to 35% when stretched uniaxially and 20% for biaxial extension. Using a combination of molybdenum metal foils, a molybdenum trioxide paste, and magnesium metal foils as electrode materials, a peak power output of 196 µW cm–2 and an energy density of 1.72 mWh cm–2 is achieved. The biodegradable batteries are used to power an on‐skin biomedical sensor patch, enabling monitoring of sodium concentration in sweat. This concept provides a versatile route for high‐power biodegradable batteries, enabling untethered soft electronic devices in a sustainable future.