Almost every electrochemical experiment is carried out in a medium consisting of a solvent and supporting electrolyte. Many such combinations have been used by electrochemical experimenters; as a glance at the Appendix will show, selection of a solvent and electrolyte has been the subject of much discussion in the literature. Yet the problem is not intrinsically complicated; a handful of solvent-electrolyte combinations would probably suffice for the majority of electrochemical applications. For this reason, a few particularly good solvent systems (the term “solvent system” is used here to describe the medium consisting of both solvent and supporting electrolyte) are recommended here, in lieu of an extended but uncritical listing of all such systems. The systems to be recommended have been chosen from among many that have been reported. However, because the novice will certainly want to develop a feel for what makes a “good” solvent system, the first part of the chapter discusses desirable criteria, as well as the ways in which electrochemical results may depend on the nature of the particular solvent-electrolyte combination employed. Because special situations frequently do require special solutions, Section III describes some less common solvents and electrolytes that have been found useful in special situations. Finally, the Appendix offers a guide to further readings of a more comprehensive nature.