1. Introduction  
2. Near-infrared observations and data reduction  
2.1. Observations  
2.2. Data reduction  
3. Results  
3.1. Photometric classification  
3.2. Excess sources  
3.3. Spectral classification of the massive stars  
3.4. Photometric vs Spectroscopic spectral type  
4. Hertzsprung-Russell diagram  
5. Discussion  
5.1. Cluster properties of W49  
5.2. Feedback  
5.3. Do massive stars in W49 form in isolation?  
5.4. W49 as an extragalactic template?  
6. Conclusions