Internal auditing is a systematic process to evaluate and improve the effectiveness of an organization's management system. It compares the actual system to requirements to identify areas for improvement. The key phases of an internal audit are preparation, proceedings where evidence is collected, reporting findings, and follow-up to ensure actions are completed. First party audits are internal audits conducted by an organization on itself, while second and third party audits involve external parties. Planning internal audits involves determining scope, frequency, and qualified auditors to evaluate processes objectively.