Optical fibers enable not only the use of optical spectroscopy where conventional spectroscopy cannot be performed, but also less common methods of interrogation, such as evanescent wave spectroscopy. The use of fibers in evanescent wave excitation, imaging and sensor arrays, in distributed sensing, and in microsensors and nanosensors is important in analytical schemes. Fiber optic sensing is applied to many fields, including medical, chemical and environmental analysis, and molecular biotechnology. In a recent review, Otto S. Wolfbeis of the Institute of Analytical Chemistry at the University of Regensburg in Germany examined many fiber optic sensors of chemical, biochemical and environmental significance, including those for gases, vapors, humidity and organic chemicals, and ion sensors and biosensors. Scientists have reported sensors for several ions as well as for the detection of toxic nerve and biological warfare agents. Researchers remain focused on several areas of development. Hydrogen and methane are of great interest because of their explosive natures when mixed with air. Sensors for carbon dioxide and ammonia are temporally unstable and sensitive to ambient gases. Optical sensing of pH remains a challenge because of cross sensitivity to ionic strength. The author also reported on applications of fiber optic sensing, including that of unstable organic compounds, on the monitoring of pollutants in wastewater, and on trace gases such as methane, acetylene, CO2, CO and H2S. In biotechnology, applications are related to the fabrication of drugs and protein and to the culture of mammalian cells and engineered tissues. Wolfbeis noted that, among several areas of active study, the success of surface plasmon resonance research in the form of fiber optic sensing is impressive. (ASAP Analytical Chemistry, online April 15, 2006.)