Contents  
1 Introduction  
2 Basic Terminology and Background  
3 Clusters in Directed Networks – Intuition and Discussion  
4 Dealing with Edge Directionality: Approaches for Identifying Clusters-Communities in Directed Networks  
5 Definition-Based Classification of Clustering Methods  
6 Evaluation Metrics and Benchmarking  
7 Real-world Applications on Directed Networks  
8 Open Problems and Future Research Directions  