Abstract: In comparison with vitrinite and liptinite,inertinite is characterized by its inert properties,especially during the carbonization process.The definition and classification of inertinite are the important components of the “ICCP system 1994”.In the classification (ICCP system 1994),the inertinite contains seven macerals and does not contain subgroups.These seven macerals include fusinite,semifusinite,funginite,secretinite,macrinite,micrinite,and inertodetrinite.The former three macerals preserve cell structures,but secretinite,macrinite,and macrinite do not have cell structures.Only those cell walls with high reflectance in the macerals with cell strcures can be identified as inertinite macerals.Two noticeable features of this classification are:① sclerotinite in the former classification was replaced by funginite and secretinite,and ② macrinite has been redefined to show a clear distinction between secretinite and macrinite.Funginite consists of fungal remains only.Although secretinite has similar optical characteristics with fungal sclerotia,it was derived from plant excretions,which have been subjected to oxidization,followed by coalification.The definition of other inertinite macerals in ICCP system 1994 remain largely unchanged with those in the old Stopes Heerlen Classification.The macerals in “ICCP system 1994” correspond to those in the Chinese National Standard “Classification of Macerals for Bituminous Coal”,but the latter contains some submacerals(fusinite was divided into pyrofusinite and oxyfusinite,and macrinite was divided into macrinite 1 and macrinite 2).The origins of fusinite,i.e.,fire,oxidation,or other derivations,remain controversial.Unlike the vitrinite classification suitable for middle-and high-rank coals,the classification of inertinite is suitable for the coals with a full coal rank,i.e.,from peat to meta-anthracite.