In this chapter, the main categories of integrated optical sensors that is grating-couplers, interferometers, photonic crystals, microring resonators, slot waveguides or silicon wires will be discussed. Emphasis will be given to the analytical performance of these sensors upon their application in clinical diagnostics, food analysis schemes or environmental monitoring. Finally, the attempts to build up lab-on-chips or portable devices for application of these sensors at the point-of-need will be mentioned. The comparison of the various types of sensors will be performed using the detection sensitivity and in particular the limit of detection (LOD) as figures of merit. The LOD is referred to the lowest amount of analyte that the sensor can detect as a signal distinguishable from the measurement noise. Usually, the LOD is expressed as refractive index units (RIU) or as surface mass density (g mm-2). It can be also expressed as analyte concentration, although this value could complicate the comparison between different sensors which have been evaluated using different analytes or recognition molecules with different affinity constants. Therefore, whenever applicable, the first two expressions of LOD are preferable to be employed as a more objective performance criterion.