Mandatory reporting laws require designated professionals—including all registered nurses—to report suspected abuse, neglect, and certain communicable diseases to appropriate authorities. These laws exist to protect vulnerable populations who cannot protect themselves: children, elderly adults, dependent adults, and individuals with disabilities. The legal standard for reporting is reasonable suspicion, not confirmed proof. The nurse is not required to investigate or prove abuse—only to report when assessment findings raise reasonable concern. Failure to report is a criminal offense in most jurisdictions. Reporters acting in good faith are protected from civil and criminal liability by statutory immunity provisions. The ethical framework supporting mandatory reporting balances patient autonomy and confidentiality against the duty to protect vulnerable populations (beneficence and non-maleficence). HIPAA permits disclosure of protected health information without patient consent for mandatory reporting purposes. Communicable disease reporting to public health authorities enables disease surveillance, outbreak detection, contact tracing, and population-level prevention interventions.