1 Introduction
2 Ad Targeting Models
2.1 Inverted Index
2.2 Age Targeting
2.3 Gender Targeting
2.4 Re-targeting
2.5 Keyword Targeting
2.6 Behavioral Targeting
2.7 Contextual Targeting
3 Retrieval Systems
3.1 Organic Retrieval
3.2 Two-Tower Network for Retrieval
3.3 Training the Two-Tower Model
3.4 Two-Tower Inference and Retrieval
3.5 Advantages of the Two-Tower Model
3.6 Challenges and Considerations
4 Comparing Ad Targeting and Organic Retrieval
5 Metrics and Experimentation
5.1 Metrics
5.2 Controlled Experimentation Framework
6 Conclusion