The field of biomolecular interaction analysis has been revolutionised over the past decade with the development of biosensors that enable 'real-time' monitoring. Characteristically, these biosensing technologies combine mass sensitive transducers, biointerfacial chemistry and the specificity of a wide range of affinity ligands. Considerable development of these elements has occurred over the past few years and promises to create a new generation of portable biosensors. The majority of transducers for 'real-time' biomolecular interaction analysis are generic evanescent wave-based mass sensors or direct mass sensors. The construction of a suitable biointerface is a key component in biosensor design and has a critical influence on the biosensor's performance. Recent developments in these areas are presented with particular emphasis on commercially available technology.