This chapter presents a literature review of theories used to frame and underpin Statistics Education Research. The aim is to describe, characterize and arrange the nature and use of theories in SER and hint at some potential trends and required directions for further theorizing the SER discipline. The review includes empirical research papers, published from 2004 to 2015, and focuses on students' learning of statistics or probability at the primary and secondary school level. The number of papers that fulfilled our inclusion criteria was 35.