These days, the implementation of novel technological platforms in biosensorbased developments is primarily directed to the miniaturization of analytical systems and lowering the limits of detection. Rapid scientific and technological progress enables the application of biosensors for the online detection of minute concentrations of different chemical compounds in a wide selection of matrixes and monitoring extremely low levels of biomarkers even in living organisms and individual cells. A biosensor is an analytical device, used for the detection of an analyte that combines a biological component with a physicochemical detector. The term 'biosensor' is often used to cover sensor devices used in order to determine the concentration of substances and other parameters of biological interest even where they do not utilise a biological system directly. The device is made up of a transducer and a biological element that may be an enzyme, an antibody or a nucleic acid. The bioelement interacts with the analyte being tested and the biological response is converted into an electrical signal by the transducer. Depending on their particular application, biosensors are also known as immunosensors, optrodes, resonant mirrors, chemical canaries, biochips, glucometers and biocomputers. Biosensor probes are becoming increasingly sophisticated, mainly owing to a combination of advances in two technological fields: microelectronics and biotechnology. Biosensors are highly valuable devices for measuring a wide spectrum of analytes including organic compounds, gases, ions and bacteria. Many optical biosensors are based on the phenomenon of surface plasmon resonance (SPR) techniques. The book Biosensors - Micro and Nanoscale Applications embodies the present state of the art and prospective options for micro and nanoscale accomplishments in biosensors construction and applications.