Droplets, bubbles or solid particles concentration and their particle size distribution markedly influence process conditions. In this article an overview in respect to popular invasive and non-invasive local measurement techniques for bubbles and droplets will be given. It starts with capillary suction probes, laser Doppler anemometry and finally covers actual developments in tomography and optical endoscopic measurement techniques. Furthermore, the possibilities and limitations of analyzing particle size distributions within different methods as well as application fields and their limits will be discussed.