Bacteriophages (phages) are viruses specific towards bacterial strains and are natural regulators of bacterial populations in nature. Interest in the therapeutic use of phages is growing due to the emergence of antibiotic resistant pathogens. Bacteriophage proteins are responsible for phage specificity and virulence. These proteins are i) adhesins, capable of recognizing specific receptors on the bacterial surface, ii) enzymes responsible for destroying bacterial cell wall components or bacterial slime, and iii) structural proteins making up the phage capsid. Bacteriophage enzymes destroy the bacterial cell wall from both outside and inside by hydrolyzing carbohydrate and protein components. All these proteins protect phage genetic material, secure injection of the phage nucleic acid into the bacterial cell, and promote phage propagation. Our better understanding of how bacterial viruses function may help to combat antibiotic resistant human pathogens and expand the use of bacteriophages to animal and plant care. Other applications may include food processing and environmental protection.