Leaf phenology is a key adaptation that allows pedunculate oak (Quercus robur L.) to persist in the temperate zone. The consequence for trees to mistime their leaf presence with respect to seasonal variation in temperature is generally thought to be a loss of productivity due to frost damage. In previous studies, the timing of these events have primarily been found to respond to temperature and photoperiod cues, mediated by underlying genes and plasticity. Part of the northern range limit of oak in Europe is insouthern Sweden, which allows us to study genetic variation where the oak experiences its latitudinally most extreme cold temperatures. In this dissertation, sources of variation in spring and autumn leafphenology within 2023, including temperature and latitude, have been described and genetic variation putatively associated with leaf phenology was investigated. Spring and autumn temperatures were significantly associated with the timing of budburst and leaf senescence respectively, but the relative contributions of these two temperature predictors could not be disentangled from latitude due to collinearity. Genetic loci putatively associated with budburst and leaf senescence were identified using genotype-phenotype association methods and significant associations between genetic variation in these loci and latitude were tested for and detected. Functions found in previous studies associated with someof the candidate loci related to host defence and drought stress. Allelic variation in budburst candidate loci may have been associated with latitude, but it is also possible that this variation is more ecotypic than clinal. Spatial patterns of variation in the leaf senescence candidate loci were more or less concordant with those of the full SNP dataset (reflective of neutral variation). In a broader perspective, the results may indicate that there is genetic variation in the Swedish oak population that may become a source of resilience to a changing climate.