The first hundred years of radiation studies have greatly clarified the chemical processes that are induced by radiation. While the fundamental ionization processes are similar in all systems, properties of the medium such as phase, polarity and composition can greatly affect the chemistry. In all systems, one needs to understand what chemical species are formed, what the internal energies are, how they are dispersed spatially, and what reactions can occur. In this review, the progress that has been made in understanding the chemistry that occurs after a radiolysis event for liquid water is outlined as an example of how progress has been made in radiation chemistry.