1. Introduction; 2. Techniques for the characterisation of physical gels; 3. The sol-gel transition; 4. General properties of polymer networks; 5. Ionic gels; 6. Hydrophobically associated networks; 7. Helical structures from neutral biopolymers; 8. Gelation through phase transformation in synthetic and natural polymers; 9. Colloidal gels from proteins and peptides; 10. Mixed gels; 11. Innovative systems and applications.