Refining an idea first promoted by Szemerényi, this article explains the modal verb Greek μέλλω as deriving from a nasal present PIE *ml̥-n-h₃- of the root PIE *melh₃ ‘to go’. The original meaning of μέλλω and infinitive would then have been ‘I am going to’, which was grammaticalised to a future tense, as happened in various other languages, including English and French. Starting from this basic meaning of μέλλω, its uses in Homer are then explored. In the present, μέλλω develops an epistemic meaning and expresses a likelihood in the present, past, or future. This development can be compared to the epistemic function of the German future with werden, the English with will or the French synthetic future. More frequent in Homer is the use of μέλλω in the imperfect, where it serves to express a prospective past, either to denote an imminent event or as a device of the all-knowing narrator to allow the reader a glimpse of later developments. Parallels of this usage are constructions like English was going to do or French allait faire.