1 INTRODUCTION  
2 CONTEXT-DRIVEN ENGAGEMENT DEFINITION  
2.1 Interaction Mode: Embodied vs. Disembodied  
2.2 Interaction Scenario  
2.3 Personal Factors  
3 AUTOMATIC INFERENCE OF ENGAGEMENT  
3.1 Data Acquisition  
3.2 Engagement Modalities and Features  
3.3 Engagement State Inference  
4 DISCUSSION AND OPEN QUESTIONS  
4.1 Context-aware Engagement Modeling  
4.2 Temporal Dynamics of Engagement  
4.3 Personalised Models and Bias  
5 CONCLUSION