Recent advances in microscopic and cell biological techniques have revealed that bacterial chromosomal DNA is folded into a compact structure occupying a relatively small part of the cell. The bacterial chromosome (nucleoid) is organized into independently supercoiled loops called domains. The structure of the nucleoid is highly dynamic, as the domain organization enables the chromosomal DNA to undergo structural changes during different cellular processes (replication, transcription, and segregation) that take place simultaneously in a bacterial cell. Small nucleoid-associated proteins (HU, H-NS, IHF, Fis, Lrp, and Dps) and the high-molecular-weight protein SMC (structural maintenance of chromosomes) facilitate compaction of chromosomal DNA by bending, bridging, and wrapping. In addition, SMC protein is involved in chromosome segregation.