A process for the production of glycolic acid or a derivative thereof comprises: reacting formaldehyde with carbon monoxide and water in a carbonylation reactor in the presence of a sulfur catalyst, said reactor operating under suitable conditions, such that glycolic acid is formed; recovering a first product stream comprising glycolic acid, impurities and a sulfur species in the carbonylation reactor; passing the first product stream to an esterification reactor where it is subjected to esterification to form an alkylglycolate and wherein the esterification is catalysed by the sulfur species recovered in the first product stream; recovering a second product stream comprising the alkylglycolate, sulfur species and impurities from the esterification reactor; separating the sulfur species from the second product stream and recycling it to the carbonylation reactor in step (a) to form a sulphur depleted second product stream; separating the alkylglycolate from the sulphur depleted second product stream in a distillation zone; and recovering the alkylglycolate and converting the alkylglycolate to glycolic acid.