‘
Main establishment’ means:
(a) as regards a
controller with establishments in more than one Member State, the place of its central administration in the Union, unless the decisions on the purposes and means of the
processing of
personal data are taken in another establishment of the
controller in the Union and the latter establishment has the power to have such decisions implemented, in which case the establishment having taken such decisions is to be considered to be the main establishment;
(b) as regards a
processor with establishments in more than one Member State, the place of its central administration in the Union, or, if the
processor has no central administration in the Union, the establishment of the
processor in the Union where the main
processing activities in the context of the activities of an establishment of the
processor take place to the extent that the
processor is subject to specific obligations under this Regulation;
GDPR Art. 4(16)