To harvest a plentiful and healthy yield of seed potatoes for trading internationally, producers have first to plant seed potatoes of the highest quality. The United Nations Economic Commission for Europe (UNECE) has drawn up an international reference quality Standard for Seed Potatoes (UNECE Standard S-1) to help producers do exactly this. The UNECE Guide to Seed Potato Field Inspection has been developed to aid countries in the application of the Standard. The Guide is recommended for use at the discretion of the Designated Authority (DA). The Standard sets common terminology and minimum requirements for certifying high-quality seed potatoes for international trade. It covers: • Varietal identity and purity • Genealogy and traceability • Diseases and pests affecting commercial quality or yield • External tuber quality and physiology • Sizing and labelling.