  We discuss strangeness production close to threshold in p+A and A+A
collision. Comparing the body of available K+, K0, K-, and Lambda data with the
IQMD transport code and for some key observables as well with the HSD transport
code, we find good agreement for the large majority of the observables. The
investigation of the reaction with help of these codes reveals the complicated
interaction of the strange particles with hadronic matter which makes
strangeness production in heavy-ion collisions very different from that in
elementary interactions. We show how different strange particle observables can
be used to study the different facets of this interaction (production,
rescattering and potential interaction) which finally merge into a
comprehensive understanding of these interactions. We identify those
observables which allow for studying (almost) exclusively one of these
processes to show how future high precision experiments can improve our
quantitative understanding. Finally, we discuss how the K+ multiplicity can be
used to study the hadronic equation of state.
