Abstract
The Madden–Julian Oscillation (MJO) and the El Niño–Southern Oscillation (ENSO) are arguably the two most important sources of subseasonal-to-seasonal variability and predictability for many regions of the Earth. Although the ENSO phenomenon is anchored over the tropical Pacific Ocean with an interannual timescale, and the MJO propagates eastwards around the globe on a subseasonal timescale, they may interact. This chapter explores the possible interactions between ENSO and MJO in both directions, starting with a review of the characteristics and theories of ENSO and MJO themselves. Subsequently, the chapter reviews how the MJO influences ENSO, how ENSO influences the MJO, how both modes interact simultaneously, and how such interaction influences the ENSO and MJO teleconnections and their global impacts.