This chapter examines one of the most critical areas of the inductively coupled plasma mass spectrometry (ICP-MS) instrument—the sample introduction system. It discusses the basic principles of converting a liquid into a fine-droplet aerosol suitable for ionization in the plasma and presents an overview of the different types of commercially available nebulizers and spray chambers. Although there has recently been significant innovation in this area, particularly in instrument-specific components custom built by third-party vendors, the fundamental design of a traditional ICP-MS sample introduction system has not dramatically changed since the technique was first introduced in 1983. Spray chambers are discussed, but the most common type is the double-pass design, where the aerosol from the nebulizer is directed into a central tube running the entire length of the chamber. There is a wide selection of nebulizers available for different applications, there is also a wide choice of customized cyclonic spray chambers, manufactured from glass, quartz, and different polymer materials.