A Scanning Mobility Particle Sizer (SMPS) is a sophisticated aerosol instrument designed for measuring the size distribution and concentration of nanoparticles and ultrafine particles suspended in air or other gases. It is a critical tool for detailed characterization of sub-micrometer aerosols. An SMPS system typically comprises two main components: a Differential Mobility Analyzer (DMA) and a Condensation Particle Counter (CPC). The DMA classifies airborne particles based on their electrical mobility, which is directly related to their size. The CPC then detects and counts these size-classified particles after they have been grown to a detectable size by condensation. This combination allows for the measurement of particles in a wide size range, commonly from approximately 2.5 nanometers (nm) up to 1000 nm (1 micrometer). The system provides high-resolution size distributions and accurate particle number concentrations, which are essential for understanding aerosol behavior. SMPS instruments are widely utilized in various research and applied fields. They are indispensable in atmospheric research for studying aerosol formation, growth, and transport, and their impact on climate. In air quality monitoring, SMPS provides crucial data on ultrafine particulate matter, which is relevant for health effects studies. Furthermore, in material science, it is used for characterizing engineered nanoparticles and assessing their properties. Its ability to provide detailed size distribution information makes it crucial for understanding the dynamics of aerosols and their environmental and health implications. Modern SMPS systems are often integrated with user-friendly software for automated data acquisition, processing, and analysis, allowing for real-time monitoring and comprehensive reporting. These systems can also be combined with other particle sizing instruments, such as Optical Particle Sizers (OPS), to extend the measurable size range, enabling characterization of aerosols across several orders of magnitude (e.g., from 10 nm to 10 µm). This modularity enhances their versatility for a broad spectrum of aerosol research and monitoring applications.