Often at privately held companies, to become a shareholder you must agree at exercise to be subject to a variety of restrictions on your rights as a shareholder. These limitations include the ability to sell shares to third parties or a covenant to vote for the founders when electing company directors.
After a grant of stock options, am I treated as a shareholder?
No. You do not become a shareholder until you exercise a stock option (i.e. exercise your right to purchase the shares).
