Aptamers are, in general, easier to produce, easier to store and are able to bind to a wider variety of targets than antibodies. For these reasons, aptamers are gaining increasing popularity in environmental monitoring as well as disease detection and disease management applications. This review article examines the research and design of RNA and DNA aptamer based biosensor systems and applications as well as their potential for integration in effective biosensor devices. As single stranded DNA or RNA molecules that can bind to specific targets, aptamers are well suited for biomolecular recognition and sensing applications. Beyond being able to be designed for a near endless number of specific targets, aptamers can also be made which change their conformation in a predictable and consistent way upon binding. This can lead to many unique and effective detection methods using a variety of optical and electrochemical means.