Conceptually, there are two related electrochemical storage mechanisms for electrochemical energy storage materials: insertion where an ion inserts into a structure on reduction and then is removed from the structural lattice upon oxidation, and conversion where there is a chemical reaction leading to a new material or phase. For some materials, each of these mechanisms may participate at different stages of the electrochemical redox process, where the kinetics for ion and electron transport can play a determinstic role regarding which process dominates at a particular state of (dis)charge. Parasitic side reactions can also make significant contributions to the function of the energy storage system, including through formation of resistive interfaces and consumption of redox active material/s. Complementary insights in distinguishing productive and parasitic processes gained from ex situ, in situ, and operando spectroscopy, diffraction and electrochemistry studies will be highlighted in this presentation.