Regulation of cellular metabolism, proliferation and differentiation implies a tight and coordinated regulation of the expression of determined sets of genes. However, tissue-specific and a developmental pattern of gene expression is not achieved by tissue specific transcription factors, rather by unique combinations of cell-type specific transcription factors and widely expressed nuclear factors. Thus, the understanding of how transcription factors, which are ubiquitously expressed, contribute to the expression of specific genes in different tissues constitutes one of the aims of cellular biology. CCAAT/Enhancer-Binding Proteins (C/EBPs) are members of the bZIP family of transcription factors which includes C/EBPα, β, δ, γ, ε, and ζ. They all possess a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. C/EBPs play important roles in cellular proliferation and differentiation in a number of cell types such as adipocytes, hepatocytes, and cells of the hematopoietic system, as well as in neuronal differentiation. C/EBPs are also critical factors involved in metabolic processes, inflammation, ovulation, and mammary gland development. The participation of C/EBPs in such a wide variety of physiological events testifies to their versatility. In fact, C/EBPs can be regulated at different levels, which include control at transcriptional, translational and posttranslational levels. This review deals with the complex regulatory mechanisms of the C/EBP family of transcription factors, which ultimately lead to their pleiotropic biological effects.