Photoemission spectroscopy is a powerful experimental technique used to study the elemental and electronic structure of materials in various states such as solids, liquids and gases. The application covers a wide range of scientific fields, with the main focus on surface chemistry and materials science. The most common forms of photoemission spectroscopy (PES) are X-ray photoelectron spectroscopy (XPS), Ultra-Violet photoelectron spectroscopy (UPS) and Angle Resolved photoelectron spectroscopy (ARPES). Let’s explore some of the fundamental aspects of this powerful tool.