Microfluidics allows the miniaturization of many processes and leads to applications that were not possible earlier or, by drastic cost- and size-reductions, enables new applications.  In this talk, we will discuss the combination of optical probing techniques with microfluidic systems and provide some examples from our research.  Currently, we are developing a new platform that integrates light sources (e.g., diode lasers and LEDs), optical waveguides, and miniaturized optical detectors with microfluidic chips for a number of bio-medical applications.  Among the examples, we will describe a novel flow cytometer based on a radical redesign of the optical excitation and detection system that can enable a truly compact, low-cost, high-performance microfluidic-based instrument.