Abstract Aerosol mass spectrometry has become an essential tool in monitoring tropospheric aerosols. Various approaches have been developed for analyzing particles that range in size from 10 nm to 10 μm in diameter, and which consist of salts, soot, crustal matter, metals, and organic molecules, often mixed together. This wide variety of particle types has generated an equally wide variety of ionization sources, which include electron impact, laser ionization, laser desorption, chemical ionization, and electron capture ionization. Some instruments are capable of single particle analysis, while others require the collection of an ensemble of particles to obtain sufficient sample for analysis. Most instruments have been designed to ionize and analyze particular classes of compounds (e.g. salts, soot, or organics). This review provides a very broad overview of the aerosol mass spectrometry field and serves as an introduction to the many papers in this issue that deal with details about specific instruments.