Although understanding natural selection in antagonistic host-parasite interactions has been a challenge for many years, direct evidence for the coevolutionary process is still scarce, particularly in relation to changes in antagonist populations over time. The underlying processes of coevolution thus remain difficult to characterise. Time-shift experiments can be used to test the performance of an antagonist population from a moment in time against the other from the same and different moments in time, revealing reciprocal adaptation in host-parasite relationships. Here we discuss how time-shift experiments together with modelling can shed new insights on the underlying processes of antagonistic coevolution.