  It is common in the study of a dizzying array of soft matter systems to
perform agent-based simulations of particles interacting via conservative and
often short-ranged forces. In this context, well-established algorithms for
efficiently computing the set of pairs of interacting particles have
established excellent open-source packages to efficiently simulate large
systems over long time scales -- a crucial consideration given the separation
in time- and length-scales often observed in soft matter. What happens, though,
when we think more broadly about what it means to construct a neighbor list?
What if interactions are non-reciprocal, or if the "range" of an interaction is
determined not by a distance scale but according to some other consideration?
As the field of soft and active matter increasingly considers the properties of
living matter -- from the cellular to the super-organismal scale -- these
questions become increasingly relevant, and encourage us to think about new
physical and computational paradigms in the modeling of active matter. In this
chapter we examine case studies in the use of non-metric interactions.
