For three months Spain has been under one of Europe's toughest lockdowns to stop the spread of coronavirus.
Prime Minister Pedro Sánchez warned that hygiene controls must be observed strictly, despite the easing.
Spain's Covid-19 death toll stands at 28,322 - the third-highest in the EU.
The state of emergency was decreed on 14 March, and for several weeks people could not go out to exercise and children were not allowed to leave their homes for any reason.
Spain normally attracts 80 million tourists a year, with tourism providing more than 12% of the country's GDP.
Opening up the holiday market again before the summer season is over is seen as crucial to the Spanish economy.
Arrivals will have their temperature taken at the airport, state if they have had the virus and provide contact details. Spain is opening up again to the rest of the EU and Schengen zone countries outside the EU.
And now Spaniards can once again enjoy unrestricted travel in their own country.
But social distancing rules remain in place: people have to stay 1.5m (5ft) apart in public, wear masks in shops and on public transport, where that rule cannot always be kept, and clean their hands frequently.
"We must remain on our guard and strictly follow hygiene and protection measures," said Mr Sánchez.
He warned of the risk of a second coronavirus wave, "which must be avoided at all costs".
Spain's land border with Portugal remains shut until 1 July, at Portugal's request.