As the number of hotels that are strongly interested in sustainability-related issues increases, the hotel industry is still seeking consensus on how sustainability can be measured and managed. One standard that provides both measurement and policies for sustainability management is ISO 14001, which is being adopted by an ever growing number of hotels, especially in Europe. Using a sample of over 2,000 independent hotels in Spain, this report analyzes the differences between those hotels that have implemented the ISO 14001 standard and those that haven’t. Also considered are the possible effects on the business results of such companies of moderating factors such as company size and the market segment in which the hotel operates. On balance the certified hotels recorded stronger sales and earnings before taxes and depreciation than those that were not certified. Certified hotels in Spain tended to be larger than uncertified properties, and certified hotels in city and beach locations enjoyed considerably stronger performance than those without the certification. The report challenges the often-heard contention that adopting sustainability programs will diminish hotels’ performance. Instead, these data show the reverse to be the case.