PF: If a researcher is residing and primarily working in country A, but is also employed in country B for one day a week, are they eligible to apply for a Postdoctoral fellowship in country B?

The researcher would be eligible to apply for a fellowship in country B. Working one day a week in a different country does not contravene the mobility rule, as it adheres to the “main activity” concept. The “main activity” stipulates that researchers must dedicate more than 50% of their employment time, which would still be upheld in this scenario.

But, if the researcher works only one day a week, leaving the other four days without a work contract, then they would not be eligible as the “main activity” would be limited to that single day of work.