Smale spaces were defined by D. Ruelle to describe the properties of the basic sets of
an Axiom A system for topological dynamics. One motivation for this was that the
basic sets of an Axiom A system are merely topological spaces and not submanifolds.
One of the most important classes of Smale spaces is shifts of finite type. For such
systems, W. Krieger introduced a pair of invariants, the past and future dimension
groups. These are abelian groups, but are also with an order which is an important
part of their structure. The second author showed that Krieger’s invariants could be
extended to a homology theory for Smale spaces. In this paper, we show that
the homology groups on Smale spaces (in degree zero) have a canonical
order structure. This extends that of Krieger’s groups for shifts of finite
type.