  We introduce the notion of the quotient of a category $C$ by the action $A :
M \longrightarrow C \times C$ of a unital symmetric monoidal category $M$. The
quotient $C/M$ is a 2-category. We prove its existence and uniqueness by first
showing that every small 2-category has a presentation in terms of generators
and relations and then describing the generators and relations needed for the
quotient $C/M$.
