Microbicides are routinely used on hard, non-porous surfaces to interrupt the spread of pathogens in a wide range of sites including healthcare, food production, restaurants, farms, veterinary clinics, homes, schools, and other commercial and institutional settings. Over the years, a number of laboratory test methods have been developed to assess the effectiveness of hard, non-porous surface microbicides. These methods have ranged from testing microorganisms in suspension to drying them on hard carriers and exposing them to the microbicide. Regulatory authorities throughout the world have relied upon data generated using these methods to approve applications/licenses for sale and distribution of these products in commerce. To date, there is no single method for this purpose that can be used and accepted in all OECD member countries. In this Guidance Document, four methods are described that permit the evaluation of efficacy of microbicides used on hard non-porous surfaces.