An overview of the electrospray processes is given and discussed, from the formation and the onset of the spray to the generation of gas-phase ions. This soft ionisation method for mass spectrometry is indeed characterized by non-equilibrium conditions, and the striking features relative to its use are difficult to be analytically or numerically modelled or even observed. In particular, the ionisation model known as the "ion evaporation model" will be largely discussed and its relevance with respect to the other model for gas-phase ions generation, the "charge residue model" will be highlighted. Lastly, the influence of the species nature and respective concentrations in the sprayed solution will be reviewed.