The Quarterly economic accounts operation anticipates the data of the Economic accounts of the Basque Country via the auxiliary information of quarterly-observed situational economic indicators. This information is modelised to obtain the quarterly estimation of the main macro-figures of the Basque economy from the viewpoints of Supply, Demand and Employment. As a result, the real quarterly evolution of the GDP of the community and its provinces is determined. The concepts and definitions of the operation are established in the European System of Accounts.