The paper by R. Guimerà, L. Danon, A. Díaz-Guilera, F. Giralt, and A. Arenas explores the self-similar community structure in organizations, focusing on the informal networks that form outside of the formal organizational chart. These informal networks are crucial for managing unexpected situations and tasks. The authors analyze the e-mail network of a real organization with approximately 1,700 employees, using the Girvan-Newman (GN) algorithm to identify communities. Their findings reveal a self-similar property in the community structure, suggesting a universal mechanism driving the formation and evolution of these networks, similar to other self-organized complex systems. The e-mail network is built by treating each e-mail address as a node and linking nodes if they exchange emails. After removing bulk e-mails and unidirectional links, the network is analyzed for community structure. The results show a power-law distribution in community size, with a cutoff at around 100 nodes, and a branching structure that resembles self-similar systems like river networks. The Horton-Strahler index further confirms the topological self-similarity of the community tree, with a bifurcation ratio of approximately 5.76. This study highlights the potential optimization principles underlying the interactions within organizations, similar to the optimization of water flow in river networks.The paper by R. Guimerà, L. Danon, A. Díaz-Guilera, F. Giralt, and A. Arenas explores the self-similar community structure in organizations, focusing on the informal networks that form outside of the formal organizational chart. These informal networks are crucial for managing unexpected situations and tasks. The authors analyze the e-mail network of a real organization with approximately 1,700 employees, using the Girvan-Newman (GN) algorithm to identify communities. Their findings reveal a self-similar property in the community structure, suggesting a universal mechanism driving the formation and evolution of these networks, similar to other self-organized complex systems. The e-mail network is built by treating each e-mail address as a node and linking nodes if they exchange emails. After removing bulk e-mails and unidirectional links, the network is analyzed for community structure. The results show a power-law distribution in community size, with a cutoff at around 100 nodes, and a branching structure that resembles self-similar systems like river networks. The Horton-Strahler index further confirms the topological self-similarity of the community tree, with a bifurcation ratio of approximately 5.76. This study highlights the potential optimization principles underlying the interactions within organizations, similar to the optimization of water flow in river networks.