H‐NS is a small chromatin‐associated protein found in enterobacteria. H‐NS has affinity for all types of nucleic acids but binds preferentially to intrinsically curved DNA. The major role of H‐NS is to modulate the expression of a large number of genes, mostly by negatively affecting transcription. Many of the H‐NS‐modulated genes are regulated by environmental signals, and expression of most of these genes is positively regulated by specific transcription factors. Therefore one of the purposes of H‐NS could be to repress expression of some genes under conditions characteristic of a non‐intestinal environment, but allow expression of specific genes in response to certain stimuli in the intestinal environment. The hns gene is autoregulated. In vivo the H‐NS to DNA ratio is fairly constant except during cold shock, when it increases three‐ to fourfold. In this review we propose that only the preferential binding to intrinsically curved DNA plays a role under normal growth conditions, and we discuss the different mechanisms by which H‐NS might affect gene expression and how H‐NS could be involved in the response to different stress situations. Finally, we summarize the evolutionary and functional relationship between H‐NS and the homologous StpA.