The use of nanoparticle beams for the preparation and characterization of isolated nanoscopic matter is reviewed. It is a general preparation scheme which is shown to be of broad use, whenever the intrinsic properties of nanoscopic matter without any interactions with other particles or substrates are of interest. The size regime spans a few nanometers up to the micron sizes, wherein a large variety of substances and materials can be studied. Similarly broad are the detection schemes and properties, which can be investigated by this approach. This review covers various properties of isolated nanoparticles, including their size, surface properties, optical constants, as well as their local electronic structure.