The Krüppel-like factor (Klfs) family of gene regulatory proteins are transcription factors implicated in many biological processes, including proliferation, apoptosis, differentiation and development. The characteristic feature of this family is the presence of three Krüppel-like zinc fingers, which bind to CACCC elements and GC-rich regions of DNA, to mediate activation and/or repression of transcription. In recent years several Klf knockout mice have been generated. The aim of this review is to outline the biological roles of those Klfs as deduced from the gene ablation studies.