How is Melatonin Synthesised?
I do not know the exact process in industry, but these are the steps that I thought of (someone likely thought of this before me, it is a very simple synthesis).  The main synthesis of the ring is done in Fischer indole conditions.  Therefore I broke up the molecule into a compound known as 4-acetamidobutanal and p-hydrazinoanisole.  The first compound is an amide that is available from the reaction of 4-aminobutanal and acetyl chloride or acetic anhydride in the presence of a base.  The latter compound is available from the reaction of p-anisidine with sodium nitrite and hydrochloric acid to form the diazonium chloride, and then reduction with sodium sulfite and sodium hydroxide.  This is just an example of a synthesis.  The overall synthesis shouldn't be more than 5 or 6 steps.  

I found an article highlighting the syntheses, you can take a look.  Apparently the synthesis that I described above is very similar to the most effective synthesis, a one-pot synthesis done in very similar conditions and having similar starting materials.