This reprint, based on the Special Issue, provides a general overview of different biosensors, briefly explaining the general approaches to identifying them, their construction, and their performance. A discussion concerning how the required components of biosensors are combined to perform analytical work is presented. Different signal-transducing mechanisms are discussed, particularly those addressing the immobilization of biomolecular components in the vicinity of a transducer interface, and their functional integration with electronic or optical devices.