In this study we will focus on the dynamics of ENSO and its interaction with tropical basins. After a short introduction of the current state of ENSO research and the open questions related to ENSO, I will focus on three aspects: (1) The ENSO phase space, which is a presentations of the core ENSO dynamics. The analysis of the phase space can help to understand how ENSO works. (2) ENSO and tropical basin interactions in idealised worlds. Here we will use a series of coupled climate models simulations with idealised configurations of land and ocean basins to illustrate how ENSO behaviour is affected by ocean basin size and the interaction with other ocean basins. (3) We will discuss the unresolved problem of how the tropical Pacific mean state is changing under global warming.