This chapter focuses on melody and harmony in popular music, particularly rock and discusses statistical, corpus-based work on rock music, alongside other theoretical and empirical work as applicable. Much of the research in music psychology has assumed the conceptual framework of "common-practice" music: Western art music of the 18th and 19th centuries. It is generally agreed that rock is "tonal" in the broad sense that every song has a tonal center—a pitch class that serves as a point of focus and stability. The chapter examines the distribution of scale-degrees in both the melodies and the harmonic progressions. Related to scales is the issue of key identification in rock; define the "key" of a song as its tonal center, without specifying major or minor. Harmony in rock has been the subject of considerable discussion. An interesting aspect of rock melody is its relationship with harmonic structure. The rhythmic aspects of a rock song must be understood in relation to its meter.