1. Background 2. Respiratory Tract 2.1 Nose 2.2 Pharynx 2.3 Larynx 2.4 Trachea 2.5 Bronchi and Bronchioles 2.6 Gas Exchange Airways 2.7 The Lymphatic System 3. How Particles Deposit in the Respiratory Tract 3.1 Sedimentation 3.2 Impaction 3.3 Brownian Diffusion 3.4 Interception 3.5 Electrically Charged Particles 4. Retention and Removal of Deposited Particles 4.1 Upper Respiratory Tract 4.2 Tracheobronchial Region 4.3 Pulmonary Region 5. Gases and Vapors 6. Literature