1. Introduction  
2. Construction of the eRASS1 Galaxy Groups and Clusters Catalog  
2.1. Source Detection  
2.2. Catalog Cleaning  
2.3. Optical Identification of eRASS1 Clusters  
2.4. Contamination Estimation via a Mixture Model  
3. Samples of Clusters of Galaxies and Galaxy Groups  
3.1. The Primary Galaxy Clusters and Groups Catalog  
3.2. The Cosmology Sample  
3.3. Purity and Completeness  
4. Comparisons with Overlapping Cluster Surveys  
4.1. Surveys in the X-ray Band  
4.2. Sunyaev Zel’dovich Effect Surveys  
4.3. Optical Surveys  
5. X-ray Properties of the eRASS1 Galaxy Clusters and Groups  
5.1. Post-Processing of the eROSITA Data  
5.2. X-ray Properties of eROSITA Clusters and Groups  
5.3. Gas Mass and Total Mass Measurements  
5.4. Comparisons of X-ray Properties with eFEDS and Chandra  
6. Population Properties of the eRASS1 Clusters  
6.1. log N − log S  
6.2. The X-ray Luminosity Function  
7. Conclusions and Summary