Fieldwork in Estonia this Fall

It depends on your situation? Will you be working for an Estonian company? Will you be here longer than 3 months? Are you here for Academic reasons or for work experience?

If you work for an Estonian company, you need to be approved of by the Estonian unemployment insurance Agency and the migration bureau, for permission to work and obtain an ID card. My piece of advice for this situation, is you will need to present credentials of your qualifications. This means having an original diploma from your college, notarized and containing an apostille from the State Dept. of State that is coincides with the Hague convention. This way they recognize it as an official document when going through the approval process.

If you are here longer than 3 months?
You need an ID card for whatever your purpose here is, Academic, Employment, or something else.

If you are here less than 3 months doing temporary work, you will still need to obtain permission from the Migration office to carryout temp. work (IF you work for an Estonian company or institution)

Those are just a few things off the top of my head, but it really depends on your personal situation.