Signed networks appear naturally in contexts where conflict or animosity is apparent. In this book chapter we review some of the literature on signed networks, especially in the context of partitioning. Most of the work is founded in what is known as structural balance theory. We cover the basic mathematical principles of structural balance theory. The theory yields a natural formulation for partitioning. We briefly compare this to other partitioning approaches based on community detection. Finally, we analyse an international network of alliances and conflicts and discuss the implications of our findings for structural balance theory.