The field of Particle Characterization is important to a broad range of commercial and academic activities, and it includes an extensive array of techniques, instruments, and applications. An attempt is made here to provide a framework for describing and assessing this complex field. This brief overview touches on three topics: the motivation for Characterization, a proposed system for categorizing work within the field, and examples of recent technological advances. The examples include photonic, ultrasonic and electrosonic measurement of particle size, tomographic determination of concentration and multiphase flow, optical trapping and AFM techniques for measuring interparticle forces, and in-line imaging techniques combined with image analysis to measure shape factors. Some of these techniques have been implemented in on-line and in-line applications. These highlights, together with the descriptive framework, provide a broad overview of the current state of the art.