As a UK seller, do I need an EORI number to sell into Germany?

Yes, you cannot proceed at customs without an EORI number. Since 1 January 2021, the UK is treated as a third country for customs purposes, as the IHK Munich sets out in their Brexit and goods movement overview, and every customs declaration requires a valid EORI registration — both for you as the shipper and often for the freight forwarder physically moving goods across the border. The UK-EU Trade and Cooperation Agreement (TCA) provides tariff-free trade in goods of British origin, but does not remove the EORI requirement. If you ship without an EORI number, you risk customs clearance delays and, worst case, the entire shipment being returned — which can be costly and time-consuming, particularly for FBA shipments to Amazon warehouses.