This guide is based on the knowledge and more than 25 years of experience on the use of room-temperature vulcanizing (RTV) silicone rubber coatings that are used to improve the contamination performance of outdoor high-voltage (HV) insulators. This guide discusses various important aspects that are needed for satisfactory long-term performance of HV insulator coatings (HVIC); namely, various application methods, pre-coated insulators, partially coated insulators, maintenance issues on coated insulators, factors aff ecting long-term performance, the question of aging, laboratory accelerated tests, and functional outdoor evaluation. However, it must be clear that for any specifi c application, judgment and experience are required to analyze and balance the many characteristics, which are discussed to obtain satisfactory performance and reliability.