Integration host factor is a sequence-specific, histone-like, multifunctional DNA-binding and -bending protein of Escherichia coli. The characterization and functional analysis of this protein has been done mainly in bacteriophage lambda and other mobile genetic elements. Less is known concerning the role of integration host factor (IHF) in E. coli, although it has been implicated in a number of processes in this organism including DNA replication, site-specific recombination, and gene expression. This review presents recent work which suggests that IHF alters the activity of an unusually large number of operons in E. coli. We discuss the possible physiological relevance of the involvement of IHF in gene expression and the hypothesis that IHF is a member of a class of functionally redundant proteins that participate in chromosome structure and multiple processes involving DNA.