  We describe a coordinate-free perspective on conformal nets, as functors from
intervals to von Neumann algebras. We discuss an operation of fusion of
intervals and observe that a conformal net takes a fused interval to the fiber
product of von Neumann algebras. Though coordinate-free nets do not a priori
have vacuum sectors, we show that there is a vacuum sector canonically
associated to any circle equipped with a conformal structure. This is the first
in a series of papers constructing a 3-category of conformal nets, defects,
sectors, and intertwiners.
