1. Land surface observations 2. Upper air observation and remote sensing 3. Data quality control and dataset development 4. Homogenization task and its principal approaches 5. Relative homogenization: The basis 6. Relative homogenization: Optional tools 7. Relative homogenization: Special problems 8. A selection of statistical homogenization methods 9. Accuracy of homogenization results 10. Use of quality controlled and homogenized data Appendix: Basic statistical concepts