The article contains a critical edition, with an annotated translation, of Isaak Argyros’ Epistola ad Kolybam, a short text of geometric metrology characterised by a complex textual tradition. The edition is preceded by an outline of the context in which the work was written. Two appendixes contain the metrological excerpts that follow the Epistola ad Kolybam in one of the two branches of the manuscript tradition and the diagrams associated with the work in representative witnesses of these two branches.