In the last few decades, there has been an increasing demand for more sensitive, cheaper and faster diagnostic tests in healthcare. Nanotechnology has the potential to revolutionise medical diagnostics by allowing rapid testing potentially in the doctor's office, greater sensitivity down to single cell or molecule level, as well as screening of diseases at an earlier stage through identification of disease biomarkers at extremely low concentrations. Nanotechnology is considered a broad area of science that incorporates multiple scientific disciplines, and can be defined as the creation and manipulation of materials, systems, and devices at the nanometer scale. The development of nanomaterials and nano-devices can be classified into two general approaches. The top down approach deals exclusively with developing nanostructures through machining, templating and lithographic techniques and refers to the fabrication and development of microfluidic and nanofluidic devices. The bottom-up approach focuses on the synthesis of nanomaterials from a single atom or molecule and relies on self-assembly or self-organization to produce particles with uniform size and shape. These micro/nanofluidic devices and nanomaterials display extraordinary physical and chemical properties which have been exploited for a large number of different novel nanodiagnostic applications. In this chapter, a general overview of nanotechnology for medical diagnostic applications will be given. The chapter will firstly define nanotechnology followed by a brief summary of bottom-up approaches to developing nanomaterials and their use in medical diagnostics. Then a discussion on the top-down approach will focus on nano-devices, methods for fabrication and the applications of these devices in medical diagnostics. The chapter will go on to review the current applications of these nanomaterials. In the final part of the chapter, the future prospects and outlooks for nanotechnology in the field of molecular diagnostics will be discussed.