Complement receptor 3 (CR3) is an integrin that recognizes several different ligands. Binding to CR3 in phagocytic cells activates signaling pathways involved in cytoskeleton rearrangement, regulation of cell motility, alteration of gene expression and phagocytosis of complement-opsonized as well as of some non-opsonized particles and pathogenic bacteria. However, CR3-mediated phagocytosis of some Gram-negative bacteria does not induce bacterial clearance. Pseudomonas aeruginosa, Salmonella and Escherichia coli are eliminated after phagocytic cell–bacteria interaction mediated by CR3. However, Bordetella takes advantage of the CR3 function and uses it to enter into macrophages leading to bacterial survival. The final fate of the pathogen is determined by combinations of host and bacterial factors, in which molecular interactions between CR3 and bacterial ligands are involved.