Nucleoid-associated proteins typically are abundant, low-molecular-mass polypeptides that bind DNA and alter its shape and its ability to participate in transactions such as transcription. Some can bind RNA and influence the gene expression profile of the cell at a posttranscriptional level. They also have the potential to model and remodel the structure of the nucleoid, contributing to chromosome packaging within the cell. Some nucleoid-associated proteins have been implicated in the facilitation of chromosome evolution through their ability to silence transcription, allowing new genes to be integrated into the nucleoid both physically and in a regulatory sense. The dynamic composition of the population of nucleoid-associated proteins in model bacteria such as <i>Escherichia coli</i> and <i>Salmonella enterica </i>links nucleoid structure and the global regulation of gene expression, enhancing microbial competitive fitness and survival in complex environments.