1. Introduction 2. Physical fractionation 2.1. Aggregate fractions 2.2. Particle size fractions 2.3. Density fractionation 2.4. High-gradient magnetic separation (HGMS) 3. Chemical fractionation 3.1. Extraction procedures 3.1.1. Dissolved organic matter (DOM) 3.1.2. Soil microbial biomass 3.1.3. OM soluble in alkali and acid: fulvic acid, humic acid and humin fraction 3.1.4. Organic solvents 3.2. Hydrolysis of OM 3.2.1. OM hydrolyzed with hot water 3.2.2. OM hydrolyzed with acids (HCl and H2SO4) 3.3. Oxidation of OM 3.3.1. OM oxidized with potassium permanganate (KMnO4) 3.3.2. High-energy ultraviolet (UV) photooxidation 3.3.3. Oxidative degradation of OM with hydrogen peroxide (H2O2) 3.3.4. Oxidative degradation of OM with disodium peroxodisulfate 3.3.5. Oxidative degradation of OM with sodium hypochlorite 3.4. Destruction of the mineral phase 3.4.1. Destruction of the mineral phase by hydrofluoric acid (HF) 3.4.2. Destruction of the mineral phase by oxidative degradation with dithionite and oxalate 4. Combinations of fractionation methods 4.1. Combined density and chemical fractionations 4.2. Combined particle size and chemical fractionations 5. Conclusions Acknowledgements References