Yes, the Eurail Pass is fully valid in Portugal and covers the national rail network operated by Comboios de Portugal (CP). You can use it on regional trains, inter-regional trains, and the urban networks in Lisbon and Porto. However, there is a significant catch: seat reservations are mandatory for the high-speed Alfa Pendular and the Intercidades (Intercity) trains. These reservations cannot always be made online through the Eurail website and often require visiting a ticket window at a Portuguese station. In 2026, rail connectivity between Portugal and Spain remains somewhat limited; the main international route is the "Celta" train between Porto and Vigo. While the pass provides great value for cross-country travel to the Algarve or Coimbra, you should budget an extra €5 to €10 per leg for those required reservation fees to ensure you have a guaranteed seat.