Medical electronic devices are an integral part of the healthcare system today and are used in a variety of applications around us. The design of such devices has several stringent requirements, the key being miniaturization, low-power operation, and wireless functionality. In this talk, I will present CMOS-based miniaturized, low-power and wireless biomedical devices in three broad domains: (a) in-vivo navigation and tracking, (b) in-vivo sensing of biomarkers and physiological signals, and (c) in-vivo stimulation and drug delivery. For the first part, I will talk about ingestible and implantable devices that can be used to achieve sub-mm tracking accuracy in 3D and in real time inside the human body, which is very useful for localizing devices in the GI tract, during precision surgeries and minimally invasive procedures. In the second part, I will present the design of a novel on-chip 3D magnetic sensor that is highly miniaturized and low-power, thus making it suitable for many biomedical applications. In the last part, I will briefly talk about my recent work on a wearable device for multi-modal sensing from sweat, followed by ongoing work on devices for stimulation and drug-delivery in the GI tract. I will end the talk with a glimpse of my future research direction.