The present festschrift volume honoring Prof. Zenobi was the perfect occasion to summarize the literature that appeared since our 2005 review of internal energy and fragmentation in electrospray ionization sources . Studying ion internal energy as a function of the ionization method and tuning parameters was often considered a niche fundamental topic, but there was a revival of interest in using the survival yield of thermometer ions to compare ion internal energies obtained from the variety of atmospheric pressure ionization methods developed over the last 20 years. The Zenobi group was very active in developing alternative ambient ionization sources and characterizing their softness through internal energy distributions ). Here we will systematically compare internal energy distributions obtained with a wide variety of ambient ionization sources. However, we will not cover all recent developments in desorption/ionization sources, or ion activation in MS/MS experiments.