We discuss the strangeness production close to threshold in heavy-ion collisions based on two independent microscopic transport approaches - HSD and IQMD - employing different in-medium scenarios for the modification of particle properties (strange mesons and hyperons) in the dense and hot medium following either from the chiral models or from a coupled-channel G-matrix approach using a meson-exchange model for strange mesons. The comparison of available kaon, antikaon and Λ data with the HSD and IQMD models shows a good agreement for the large majority of observables when incorporating the in-medium effects. The investigation of the reactions with help of transport models reveals the complicated multiple interactions of the strange particles with hadronic matter which shows that strangeness production in heavy-ion collisions is very different from that in elementary interactions. We discuss how a variety of 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 reactions.