Abstract: Compositions having antimicrobial activity against a variety of microorganisms, including vegetative bacteria, bacterial spores, fungi, and fungal spores are particularly useful for microbiocidal treatments of a variety of substances. More specifically, compositions have antibmicrobial activity against microorganisms of the Bacillus cereus group such as Bacillus cereus, Bacillus mycoides, Bacillus anthracis, and Bacillus thuringiensis are particularly useful. Compositions including hydrogen peroxide, a carboxylic acid, and a peroxycarboxylic acid in which the weight ratio of the peroxycarboxylic acid to the hydrogen peroxide is at least 4:1 are effective against microorganisms, particularly bacterial spores. Such compositions include a reduced amount of hydrogen peroxide relative to the amount of peroxycarboxylic acid as compared to conventional compositions. Compositions can also include a quaternary ammonium compound, a stabilizing agent, a surfactant, a hydrotrope, or other additives.