In the environment, temperature can vary extensively over different time scales (between seasons, over days, day/night or shorter). Temperature affects all biological processes, but importantly not in a uniform manner. In general, diffusion is less temperature-dependent than the diverse enzymatic reactions, each of which is characterized by a distinct temperature profile. Therefore, homeostatic cell function after temperature change presumably depends on a rather complex regulation of cellular processes in poikilothermic organisms. The understanding of how cells can adjust over an often surprisingly wide temperature range is limited, and the molecular basis of their acclimation limits is usually not known. In comparison to heat responses, the molecular adjustments in response to temperatures below the optimum are poorly understood. We exploit comprehensive approaches in the fly Drosophila melanogaster which is particularly amenable to efficient and precise experimentation. By working primarily with early embryos and cultured cells, we focus on cellular responses, avoiding convolution by higher levels (behavioral and organs system responses). By in vivo imaging with transgenic embryos we characterize the effects of low temperature on cellular structures including microtubules, which are known to have pronounced cold sensitivity. Deficiency screening is used to identify genes crucial for survival of low temperature during early embryogenesis, the most cold-sensitive stage of the Drosophila melanogaster life cycle. In addition, we study the transcriptional response to low temperature and address regulatory mechanisms. We apply genome-wide RNAi screening for genes important for low temperature acclimation of cultured cells.