The document discusses strategic network formation and pairwise stability in networks. It provides some basic intuition about modeling network formation as individuals making choices to form links based on costs and benefits. Links may be undirected or directed. Networks can be modeled as a game where each node announces links and a link only forms if both nodes name each other. A network is pairwise stable if no node benefits from removing a link and no two nodes both benefit from adding a new link. An example of collaboration networks with negative externalities is provided, where the network evolves from an empty network to a fully connected network due to individual link formation incentives.