What written tests are required to become a ground instructor? What are the written tests required to become a ground instructor? Do I have to take the FOI, BGI and IGI? Or just the FOI and IGI tests? 

I got confused if I should take the whole three tests - FOI, BGI, IGI - or if just the two IGI and FOI tests are enough?
The FAA offers some nice guidance here 



You may also want to check out my answer (a very close to dupe) here.