The national security of a country is the bedrock of the life of its people and the fundamental interests of the nation.It is essential for teenagers, the future and hope of a country, to learn more about national security as they will be able to shoulder the mission of China's rejuvenation when armed with an awareness of national security, the rule of law, and love for the motherland.This textbook serves as a teenager-oriented introduction to national security and the legal system for Hong Kong to safeguard national security, suitable for primary and middle school students to read and learn.