1. Introduction  
2. Observations and Data Analysis  
2.1. XMM-Newton Data Analysis  
2.2. Spitzer Data  
3. Results  
3.1. Sensitivity of the Survey  
3.2. Completeness and Contamination  
4. The Population of Young Stellar Objects  
4.1. X-ray Spectra and Luminosities  
4.2. Comparison with the ONC  
4.3. Spatial Distribution of PMS Stars  
5. Identification of Three Class III Rich Clusters Towards the Orion A Cloud  
6. Conclusions