1 Introduction
1.1 Domain Generalization for Medical Image Analysis
1.2 Our Contributions
2 Background 
2.1 Problem Definition
2.2 Settings of Domain Generalization
2.3 Related Machine Learning Tasks
3 Methods
3.1 Data-level Generalization
3.2 Feature-level Generalization
3.3 Model-level Generalization
3.4 Analysis-level Domain Generalization
4 Domain Generalization Under Limited Source
4.1 Single-source Domain Generalization
4.2 Open-set Domain Generalization
4.3 Other Under-explored Domain Generalizations
5 Future Directions
5.1 Source-limited Domain Generalization
5.2 Medical Foundation Model
5.3 Benchmark Datasets
5.4 Suggestions for Domain Generalization for Medical Image Analysis
6 Conclusion