Formula one factories began to re-open this week after serving mandatory closures.
Within the one-month gap between the Hungarian and Belgian grands prix, teams agreed to close their doors for two full weeks as a cost-cutting measure.
The first teams to shut down at the stroke of midnight after the Hungaroring race were McLaren, Mercedes, Williams and Sauber, so those teams were eligible to re-open on Monday.
McLaren test driver Gary Paffett marked the end of the shutdown by working in the Woking based team's simulator, and he will be back in action on Tuesday.
And Williams said the first tasks when its Grove headquarters got back up and running was stripping the Budapest-spec cars "in prep for Spa".
Cosworth's F1 division re-opens on Tuesday, and HRT on Wednesday.
Ferrari and Toro Rosso will remain closed until next Monday, and a day later Red Bull, Renault and Force India will re-open.
"We will be on holiday, but that does not mean our brains will stop working," said Ferrari's Stefano Domenicali recently.
"Maybe one can even find fresh inspiration when outside the normal working environment and I expect this time to be a fertile one for ideas, which when all is said and done, are what make the difference," he added.