We propose iSkin, a novel class of skin-worn sensors for touch input on the body. iSkin is a very thin sensor overlay, made of biocompatible materials, and is flexible and stretch- able. It can be produced in different shapes and sizes to suit various locations of the body such as the finger, forearm, or ear. Integrating capacitive and resistive touch sensing, the sensor is capable of detecting touch input with two levels of pressure, even when stretched by 30% or when bent with a radius of 0.5 cm. Furthermore, iSkin supports single or mul- tiple touch areas of custom shape and arrangement, as well as more complex widgets, such as sliders and click wheels. Rec- ognizing the social importance of skin, we show visual design patterns to customize functional touch sensors and allow for a visually aesthetic appearance. Taken together, these contri- butions enable new types of on-body devices. This includes finger-worn devices, extensions to conventional wearable de- vices, and touch input stickers, all fostering direct, quick, and discreet input for mobile computing.