This chapter deals with cash (banknotes and coins), the oldest and most traditional form of money in existence. Cash involves a paradox: On the one hand, it is technologically less advanced that modern means of payments like cards and apps, so one could presume that it should decline in use and eventually disappear. On the other, however, evidence for almost the whole world shows that the demand for cash is increasing, although it is used less frequently for certain types of transactions like online commerce, retail stores, and restaurants. Criminal activities may explain part of the puzzle, but not much. One advantage of cash is that it can be seen and touched, therefore appealing to the senses and conveying a sense of security. Another is that it ensures absolute privacy of transactions. Other important characteristics explaining the popularity of cash are that it is simple (it requires no technology or complication whatsoever); definitive (it instantly settles any financial obligation); private and personal (it appeals to the desire of confidentiality); and self-sufficient (it does not depend on any other infrastructure functioning). We conclude therefore that physical cash is a useful complement of a robust and diversified monetary system, in which digital means of payments gradually prevail.