For which type of transaction is a Social Security number mandatory?

A Social Security number is mandatory when applying as an individual due to the identification requirements set forth by various financial and regulatory entities. The Social Security number serves as a unique identifier for individuals, making it essential for tax reporting and verification purposes. This is particularly important in the context of investment activities, as it helps to ensure that the individual's identity is properly linked to any financial accounts or transactions.

Other types of entities, such as corporations, partnerships, and sole proprietorships, typically use an Employer Identification Number (EIN) instead when registering or conducting certain business transactions, which is distinct from individual applications requiring a Social Security number.