Computer programming is more than a tool for the artist. Writing code is manipulating a medium: a medium that is like no other. This chapter discusses the importance of coding and shows how it is enabling principled investigations into inventing new forms, creating new experiences and extending the nature of engagement with art works. It shows how formal ways of making art, from perspective to the 20th century use of systems, geometry and mathematics, have pointed to the value of programming. This is a direction that has defined the work of a range of artists. The chapter discusses the use of the medium of code by artists who talked about their art making process. They include pioneers Aaron Marcus, Harold Cohen and Manfred Mohr and other artists, some of whom are live coding practitioners.