Quantum dots (QDs) are hybrid organic/inorganic nanoparticles with novel physical properties. QDs have two components: an inorganic core and an optically active coated shell. Moreover, surface coatings can be applied to QDs to modify the particle as needed for experiments. Hydrophilic coatings prevent leaking of metal cargo from the core, enhancing the solubility in biological contexts and bind molecules, such as receptor–ligands, antibodies, therapeutic, and diagnostic macromolecules for enhanced effects. Their high surface-to-volume ratio allows multiple functional groups to attach onto the surface of the particles at constant surface volume. Silicon-, gallium-, indium-, or germanium-based; cadmium-based; and carbon-based QDs have already been used in many applications, such as imaging probes for the engineering of multifunctional nanodevices. Superior properties of QDs make them an excellent system in technology and biotechnology. This book describes electroanalytical applications of QD-based nanobiosensors, including brief information about the synthesis and characterization of QDs and basics of electroanalytical methods, followed by QDs in electrochemical biomimetic sensors, QDs in microchips, inorganic materials doped QDs, QD-based electrochemical DNA biosensors, electroluminescence for biomarker analysis using aptamer-based QDs, QD-based photoelectrochemical techniques, enzyme-based nanobiosensors using QDs, QD-based electrochemical immunosensors, and QD-modified nanosensors in drug analysis.