  We give a broad overview of a construction of a theory for matter on fixed
causal set backgrounds. We introduce the Sorkin-Johnston formalism for a free
(real) scalar field theory that is applicable to regions of continuum
spacetimes as well as to causal sets. We show examples in the causal set,
starting from the construction of Green functions to obtaining unique two-point
functions using this formalism. We also mention other approaches that have been
explored in constructing dynamics for matter on causal sets, including ideas
for interacting theories and fermions.
