IF: How do I apply the mobility rule?

If you are applying for an Individual Fellowship of the MSCA and are unsure about how to apply the mobility rule, keep in mind that the only two elements which are relevant are
the place of residence and
the place of carrying out the main activity.
While the reality of at times complex working relationships or structures can lead to misunderstandings or make it difficult to judge a particular case, these are nevertheless the two elements which make up the mobility rule. If you have doubts about your eligibility, check either with your National Contact Point or with the Research Enquiry Service