This Guide introduces seasonal adjustment and gives practical guidance to national statistical offices in producing seasonal adjusted monthly or quarterly time series covering all steps in the production process, from the evaluation of the original data series to the dissemination and communication of the seasonally adjusted series. The Guide can be used in introducing new staff to seasonal adjustment, in training courses or as a complement to other material on seasonal adjustments. The Guide is based on the use of JDemetra+ which is an open source software for seasonal adjustment.