There are plenty of restrictions in various countries. In the US, degree status does not matter. You cannot practice as an engineer without a PE qualification, issued by the state in which you practice. In Germany, you cannot open an “Engineer's Office” unless you have a German engineering degree (it actually has to say -Ing). (There are ways around it. I have a German colleague whose engineering PhD is from York. He became CEng through the IET, and Eur Ing, and started his solo engineering consulting company, but it is not an “Engineer's Office”.) On the other hand, none of my three degrees count for the IET (one British is too early at 1973; two US further degrees don't) I qualify through accomplishment. I have also supervised a number of engineering PhD degrees. But in Germany I am still not legally an engineer and cannot be unless I go back to school or someone gives me a hon. caus. 

There are plenty of restrictions in various countries. In the US, degree status does not matter. You cannot practice as an engineer without a PE qualification, issued by the state in which you practice. In Germany, you cannot open an “Engineer's Office” unless you have a German engineering degree (it actually has to say -Ing). (There are ways around it. I have a German colleague whose engineering PhD is from York. He became CEng through the IET, and Eur Ing, and started his solo engineering consulting company, but it is not an “Engineer's Office”.) On the other hand, none of my three degrees count for the IET (one British is too early at 1973; two US further degrees don't) I qualify through accomplishment. I have also supervised a number of engineering PhD degrees. But in Germany I am still not legally an engineer and cannot be unless I go back to school or someone gives me a hon. caus.