Article 3(1) lists seven categories of essential entity. Large entities in an Annex I sector are only the first of them, which is why the common shorthand "large plus Annex I" is an incomplete test; the list also covers entities a member state had identified as NIS1 operators of essential services before 16 January 2023. Important entities are the residual category under Article 3(2). The size thresholds come from Commission Recommendation 2003/361/EC: an entity is medium-sized once it has at least 50 staff, or exceeds both the €10 million turnover ceiling and the €10 million balance-sheet ceiling, and large at 250 staff, or above €50 million turnover and €43 million balance sheet. Annex I lists 11 sectors, Annex II lists 7. DNS service providers, TLD name registries, and qualified trust service providers are in scope regardless of size. Partner and linked enterprises count towards the thresholds under Article 6 of the Annex to that Recommendation, so group figures are aggregated.