The scope of this book deals with biosensors and microarrays that take advantage of the specific biological recognition between a surface-immobilised "probe" and a biological "target" in solution. In order to preserve the integrity of the biological interaction taking place on a sensor, surface immobilisation of the probe should guarantee the preservation of the probe conformation, orientation and availability. Herein, we will first give a brief definition of biosensors and their requirements. The use of organosilanes as anchoring layers for biomolecules on different materials is then discussed. Finally, the biofunctionalisation of organosilanes and their applications are described.