This paper introduces and studies the maximum k‐plex problem, which arises in social network analysis and has wider applicability in several important areas employing graph‐based data mining. After establishing NP‐completeness of the decision version of the problem on arbitrary graphs, an integer programming formulation is presented, followed by a polyhedral study to identify combinatorial valid inequalities and facets. A branch‐and‐cut algorithm is implemented and tested on proposed benchmark instances. An algorithmic approach is developed exploiting the graph‐theoretic properties of a k‐plex that is effective in solving the problem to optimality on very large, sparse graphs such as the power law graphs frequently encountered in the applications of interest.
