The High Arctic, with its low number of species, is characterised by a relatively simple ecosystem, and the vertebrate predator-prey interactions in the valley Zackenbergdalen in Northeast Greenland are centred around the collared lemming Dicrostonyx groenlandicus and its multiple predators. In this chapter, we examine these interactions in a climatic context through the predator-lemming model developed for the more southerly Greenlandic site, Traill empty set (Gilg et al., 2003, Science 302, 866-868), parameterised by means of data from the BioBasis monitoring programme to reflect the situation in Zackenbergdalen. Despite large differences in relative predator densities between these two locations, the two lemming populations exhibit remarkably similar and synchronous population fluctuations. Also, in both lemming populations the annual fluctuations seem primarily driven by a 1-year delay in stoat Mustela erminea predation and stabilising predation from the generalist predators, in Zackenbergdalen mainly the arctic fox Alopex lagopus. In Zackenbergdalen, however, the coupling between the specialist stoat and the lemming population is relatively weak. During summer, the predation pressure is high, and in most years so high that the lemming population declines during summer. This heavy predation pressure is also reflected in the summer behaviour of the lemmings, and lemmings spend most of their time under ground, and when above, they devote equal amounts of time to being vigilant and foraging. In most winters, predation by the only remaining predator, the stoat, is insufficient to regulate the lemming population. In the predator-lemming model, seasonality plays an important role in determining the. growth rate of the lemming population as well as the density of the various lemming predators. We therefore examined how variation in the relative length of seasons affected the pattern of fluctuation in the lemming population by gradually advancing or delaying the time of onset of winter. In contrast to advanced winter onset, delayed winter onset led to increased periodicity. The climatic conditions, hence, affect not only the seasonal but also the inter-annual dynamics of the collared lemming population in Zackenbergdalen