29.1. Introduction. The present chapter explains the concept of seasonal adjustment of data, its key features and main approaches, including revision policy and quality issues in general terms. It then provides some examples of country practices in the application of seasonal adjustments to international merchandise trade data. It is based on IMTS 2010 (para. 11.3), which encourages countries to compile and publish, where appropriate, seasonally adjusted monthly and quarterly international merchandise trade data on a regular basis. It is related to chapter XXVI on dissemination.