The discovery of single key players in social networks is commonly done using some of the centrality measures employed in social network analysis. However, few methods, aimed at discovering sets of key players, have been proposed in the literature. This chapter presents a brief survey of such methods. The methods described include a variety of techniques ranging from those based on traditional centrality measures using optimizing criteria to those based on measuring the efficiency of a network. Additionally, we describe and evaluate a new approach to discover sets of key players based on entropy measures. Finally, this chapter presents a brief description of some applications of information theory within social network analysis.