Spectroscopic measurements at infrared and visible wavelengths are widely used as a tool for laboratory analysis. Due to technological improvements, more and more possibilities are opened for making similar methodology feasible for direct on-line process measurements in harsh industrial conditions or small portable equipment. New optoelectronic components together with compact design can even be used to realize integrated sensor-like analyser devices. Array and multiple-wavelength detectors reduce the need for mechanisms for wavelength multiplexing and offer the possibility of simultaneous measurement of several wavelength channels. The use of narrow-band semiconductor sources gives advantages for modulation arrangements. Using array sources, electronic wavelength scanning becomes possible in some applications. The increased real-time signal-processing capability can be used to implement more complex measuring principles and efficiently compensate for disturbing effects. Instead of using only a few wavelengths, a whole spectral band analysis can be employed. As an example, real-time multielement analysis, with complex calibration functions, becomes a feasible industrial methodology. The fields of application for infrared analysers can be found in chemical process industries, food industries, energy production, and environmental protection. Portable and integrated sensor-like analyser components substantially increase application markets.