The establishment of common guidelines for seasonal adjustment within the European Statistical System is an essential step towards a better harmonisation and comparability of infra-annual statistics, especially Principal European Economic Indicators (PEEIs). Following the first 2009 edition which has been widely accepted and implemented, the 2015 revised ESS Guidelines on Seasonal Adjustment, endorsed by the ESS Committee in November 2014, present theoretical aspects and practical implementation issues in a friendly and easy to read framework, thereby addressing both experts and non-experts in seasonal adjustment. The ESS Guidelines on Seasonal Adjustment foster the transparency of seasonal adjustment practices by encouraging the documentation of all seasonal adjustment steps and the dissemination of metadata on seasonal adjustment, and foster the development of expertise and capacity building. The revised guidelines include new sections, describe better the different steps in seasonal adjustment, and specify in more details alternative practices.