You cannot have more than 100 shareholders and they cannot be foreign. On top of that, your shareholders need to be individuals, estates, or certain trusts. If they are partnerships, corporations, or nonresident alien shareholders, then they cannot qualify as adequate and qualified shareholders. Also, the S Corp needs to be a domestic corporation. You need to have only one class of stock. Finally, make sure that your company is not an ineligible corporation, like insurance companies.