1. Introduction  
2. X-ray, optical, and near-infrared data  
3. Measurement of cluster candidate counterparts in the optical and near-infrared  
4. The eRASS1 identified cluster and group catalog  
5. Quality assessments of the eRASS1 catalog  
6. Number densities and mass limits  
7. Purity of the eRASS1 cluster catalog  
8. Photometric redshift accuracy  
9. The richness – velocity dispersion scaling relation  
10. Summary