ISO 31-8 is the part of international standard ISO 31 that defines names and symbols for quantities and units related to physical chemistry and molecular physics.

In the tables of quantities and their units, the ISO 31-8 standard shows symbols for substances as subscripts (e.g., c_B, w_B, p_B). It also notes that it is generally advisable to put symbols for substances and their states in parentheses on the same line, as in c(H₂SO₄).

This annex contains a list of elements by atomic number, giving the names and standard symbols of the chemical elements from atomic number 1 (hydrogen, H) to 109 (unnilennium, Une).

The list given in ISO 31-8:1992 was quoted from the 1998 IUPAC "Green Book" Quantities, Units and Symbols in Physical Chemistry and adds in some cases in parentheses the Latin name for information, where the standard symbol has no relation to the English name of the element. Since the 1992 edition of the standard was published, some elements with atomic number above 103 have been discovered and renamed.