Today's scientists face a bewildering array of standards they should adopt to ensure effective communication across different formats (different journals, books, and electronic media). This guide helps authors recognize which symbols have the IUPAC impramatur and which should be avoided for clarity. This guide still has deficiencies. For example, it has very few guidelines for the different arrows employed to denote different sorts of reactions. Different usages are common in the literature, and it would be best if IUPAC would unify the field.