Physiologically, urine and the urinary tract are maintained sterile because of physical and chemical properties of urine and the innate immune system's action. The urinary tract is constantly exposed to the invasion of microorganisms from the exterior environment, also because of the anatomical placement of the urethra, in the vicinity of the rectum. Particularly vulnerable to urinary tract infections (UTI) are women (an additional risk factor is pregnancy), but also the elderly and children. The main pathogens causing UTI are bacteria; in 70-95% of cases it is the bacterium Escherichia coli. Infections caused by viruses and fungi are less common and are associated with decreased immunity, pharmacotherapy, or some diseases. Bacteria have evolved a number of factors that facilitate the colonization of the urinary tract: the cover and cell membrane antigens O and K1, lipopolysaccharide (LPS), fimbriae, pile and cilia. On the other hand, the human organism has evolved mechanisms to hinder colonization of the urinary tract: mechanisms arising from the anatomical structure of the urinary tract, the physicochemical properties of the urine and the activity of the innate immune system, also known as non-specific, which isolates and destroys pathogens using immunological processes, and the mechanisms for release of antimicrobial substances such as Tamm-Horsfall protein, mucopolysaccharides, immunoglobulins IgA and IgG, lactoferrin, lipocalin, neutrophils, cytokines and antimicrobial peptides. This review aims to analyze the state of knowledge on the mechanisms to maintain the sterility of the urinary tract used by the human organism and bacterial virulence factors to facilitate the colonization of the urinary tract.