Intensive research in micro/nano biosensors has resulted in a variety of sensors for monitoring different analytes for applications ranging from environmental pollutants to neuroscience. Although several biomedical sensors have been tested on animals, they are yet to reach the stage of continuous and reliable patient monitoring. For onsite impact, it is therefore imperative to transfer the sensor technology developed in the laboratories to a clinical setting to facilitate medical diagnostics in order to aid and guide treatment regimes. This chapter will elaborate on electrochemical micro/nano biosensors and wireless sensors utilized for implantation within the human body to measure the concentration of analytes, biomolecules, drugs or physical parameters such as temperature, pressure and so on. Sensor parameters such as sensitivity, selectivity, biofouling, biocompatibility, sterility and toxicity will be addressed. To address some of the previously mentioned issues, dialysis electrodes and ex vivo monitoring through blood sampling have also been considered. In addition, hurdles that need to be overcome to produce implantable micro/nano biosensors capable of continuous monitoring of analytes from a human subject will be discussed.