A substantial investment is typically one that is large enough to ensure the success of the business and is proportionate to the overall cost of establishing or purchasing the enterprise. There is no specific dollar amount set by the U.S. government, but the investment should be more than a marginal one. The business itself should be a legitimate and active commercial or entrepreneurial undertaking.

Yes, the U.S. Department of State maintains a list of countries that have treaties with the United States allowing their citizens to apply for the E-2 visa. This list is subject to change, and it's crucial to check the latest information to ensure eligibility. Not all countries have such treaties, so it's essential to verify the specific requirements based on your country of citizenship.

Yes, spouses and unmarried children under the age of 21 of E-2 visa holders are eligible to accompany them to the United States. Spouses are generally allowed to work in the U.S. by obtaining employment authorization, while dependent children can attend school. It's important to note that family members must apply for and obtain their own derivative E-2 visas.