The objective of this study is to assess the inactivation kinetics of MS2 phage (as a surrogate for enteroviruses), Bacillus subtilis spores (as a surrogate for pathogenic bacterial spores) and Cryptosporidium parvum oocyst with single and sequential disinfection strategies using ultraviolet (UV) light, ozone and free chlorine. This manuscript focuses on experimental results obtained for the inactivation kinetics of MS2 phage in natural and synthetic water with single-step UV light and free chlorine, and sequential UV/free chlorine disinfection processes. Includes 15 references, figures.