1 Introduction
2 Definition of Multimodal Graphs
3 A Taxonomy of MGL
3.1 Multimodal Graph Convolution Network
3.2 Multimodal Graph Attention Network
3.3 Multimodal Graph Contrastive Learning
3.4 Other Methods
4 MG Libraries and Applications
4.1 Multimodal Knowledge Graphs
4.2 Multimodal Biomedical Graphs
4.3 Multimodal Brain Graphs
5 Challenges and Outlooks
5.1 Data Imbalance across Modalities
5.2 Trustworthy Multimodal Alignment
5.3 Temporal Multimodal Graph Learning
5.4 Computational Efficiency of Large-Scale MGs
6 Conclusion