Are you occupied in several countries, working for one or more employers ? How to determine the country in which you are obliged to adhere to social security and pay social contributions ?
In any case, European rules do foresee that you can only be subject to the legislation of one sole country.
The solution depends on the place where you exercise a substantial part of your activities. If this place is in your country of residence, the legislation of this country will govern your situation.
But if a substantial part of your activities is outside your country of residence, the situation will be a little more complex. To read more about this and the formalities to respect, please read the Cross Borders contribution (in French language) to the Les Frontaliers website in the Sachez-Le! post of 24 October.
