Tourist seasonality consists of an imbalanced tourist activity over the course of the year. This variation has become one of the main problems facing the tourist sector, as it constitutes a major threat to sustainable growth, destination image, and loyalty, especially with respect to large-scale, well-established destinations. In this paper, our purpose is to identify seasonality determinants for the main markets of origin in Spain (i.e. British, German, and French market origins). To this end, a dynamic model has been used for a provincial panel data set during the 2006-2015 period. The Xtabond2 model has been largely used, as it combines natural and non-natural explanatory variables. The results show that the inertial factor, economic variables (income levels and relative prices), and climatic variables (temperatures differences between the destination and the place of origin) are significant determinants, together with several differences among the main markets. It is hoped that the findings of this research will be able to assist public and private organisations in developing their predictions and especially with respect to designing anticipatory correcting policies. Keywords: seasonality; markets; dynamic panel data model; GMM estimators; Spain