Solvents are a major class of commodity chemicals that are used widely in many contexts. Although important to industry, as volatile organic compounds (VOCs) there is an obvious environmental hazard associated with solvents. Furthermore, they are typically made of fossil resources and can be flammable or toxic. This chapter defines what a solvent is and gives examples of typical types of solvent and their uses. Also explained is the concept of sustainability, and its relevance to the chemistry of solvents.