This is a book about the hybridity of computing and drawing. It would seem prudent, therefore, to begin by addressing, simply, “what is drawing?” and “what is computing?” However, both of those terms are associated with contested histories, multiple creative and scientific cultures, and various colloquial and literal definitions, which are often at odds with each other. Both computing and drawing are disciplines in their own right, and both terms define sub-cultures within the discipline of architecture. As a result, it is not possible to exhaustively explore both terms, though it is possible for the hybridity between computing and drawing to bring clarity to each in terms of method, meaning, and knowledge. This chapter proceeds by articulating a series of anti-definitions, that articulate some important limitations on computing and drawing. These include: a drawing cannot be edited; a computer cannot draw; and a drawing is not final. Some algorithms are presented for the articulation of primitive marks and the first two exercises—coding a mark and drawing from a function library—are articulated.