Are non-US citizens restricted from receiving security clearances?

Non-U.S. citizens are generally restricted from receiving security clearances due to the need for a clear allegiance to the United States and the protection of national security interests. Security clearances are fundamentally based on the trustworthiness and reliability of individuals who will have access to sensitive information. U.S. citizenship is a key factor because it establishes a legal and permanent bond to the country's laws and security.

In most cases, only U.S. citizens are eligible for the highest levels of access to classified materials, particularly those that involve national defense and security programs. This ensures that individuals who are privy to sensitive information are fully accountable to national laws and can be vetted adequately by the governmental security apparatus. While specific exceptions may exist for certain roles or in cases where individual assessments suggest a valid justification, these instances are quite limited and do not change the overall restriction on non-citizens typically holding a clearance.

The provided answer reflects this principle of security and national allegiance that underpins the security clearance process.