Scientists working with nanoparticles commonly characterize them by simply a dimension.  This should be extremely unsatisfying to a chemist—chemists should prefer to know the chemical formula and ideally the structure of a chemical material.  This is challenging analytical chemistry.  This lecture will describe some progress and directions for the analytical chemistry of small gold and other nanoparticles.   Recent success stories are the nanoparticles Au25L18 and Au144L60 where L is an organothiolate ligand, relying especially on mass spectrometry but also other tools to inform about composition and structure   Another part of the story is the variability of properties with size, as these nanoparticles cross the metal-to-molecule dimension. The lecture will include the beginnings of analogous ventures into other kinds of small nanoparticles, such as silica and metal oxides.