Who decides date of eid?

Answer 1

I'm assuming the reference is to the end of the month of fasting. Supposedly, a month ends when two adult males witness the crescent of the New Moon. This is usually about two days after the new Moon date on the calendar. In practice, in these days of mass communications, some central authority takes over putting out the word. However, if you were somehow out of contact and wanted to be strictly observant, sighting the crescent Moon would do it.