The article describes how the topical issue of the journal Analytical and Bioanalytical Chemistry (ABC) is devoted to Photo Ionization in Mass Spectrometry. A large variety of widely used analytical methods and technologies evolved from these initial studies on ionization by either photon molecule or laser pulse surface interactions. A schematic time-of-flight mass spectrometer and some photo ionization (PI) techniques used in analytical mass spectrometry are depicted in the article. The scientific contributions in this special issue on photo ionization mass spectrometry are ordered according to the type of contribution. The introduction of the paper in this editorial, however refers the samples matrix and the ionization region pressure. Starting with solid and particulate samples, using laser desorption ionization (LDI), matrix-assisted laser desorption/ionization (MALDI), and finally LD (laser desorption) for sampling of surfaces and aerosol particles.