Biosensors transform physiological or biological information into electrical measurements using electronic circuits. The detected information is transmitted remotely to a data acquisition platform or a server using a wireless link for real-time monitoring and analysis. The main applications of biosensors are in wearable and implantable biomedical devices. The label-free biosensors using electrochemical and electrical transduction mechanisms such as potentiometric, amperometric, field-effect transistor, resistive, capacitive, and inductive can be developed in a small package to enable miniature point-of-care devices. The electrical properties of the biosensors are converted into voltage, frequency, or phase using various interface or readout circuit techniques. This chapter discusses the design of biosensors with wireless links for implantable or wearable sensors. A complete design example including a capacitive pH-sensor device will be discussed. The recent developments of implantable or wearable sensors using a wireless link, such as implanted wireless blood-glucose sensors, wireless capsules, and other wireless wearable devices will be presented.