Forty-seven different animal wastes were characterized using chemical and organic matter fractionation methods (water extraction and Van Soest method) and 224-day incubation studies to assess their decomposition in soil. Simple correlation and multiple factor analysis were performed to establish relationships between the composition of these wastes and C and N mineralization. Carbon and N contents ranged from 101 to 469 mg C kg−1 dry matter (d.m.) and from 4 to 39 mg N kg−1 d.m. Soluble C and N represented less than 9% of organic C and 1.5% of total N at 20°C, respectively. The C fractions soluble at 100°C or in neutral detergent were larger and represented 14 and 32% of the organic C, respectively. The hemicellulose-like (HEM) and cellulose-like (CEL) fractions contained about 16.5 and 6% of the organic N, respectively. The C distribution in the lignin-like (LIG) and CEL fractions was comparable, but the former contained more N. Carbon mineralization varied from 5 to 62% of the organic C added during the 224-day incubation; 70% of the wastes induced net N mineralization at the end of incubation (from 3 to 51% of organic N). Other wastes induced net soil inorganic N immobilization, from −1 to −31% of the organic N added. Most highly significant correlations were established between the C mineralization and the C present in the water-soluble fraction at 20°C, and the HEM and LIG fractions. Relationships between N mineralization and biochemical characteristics were weak, except with the soluble Van Soest fraction, and highly significant correlations were observed between N mineralization rates calculated at 224 days of incubation and the organic N content or C/N ratio of wastes. Finally, an objective hierarchical classification based on composition criteria and C and N mineralization led to the definition of six different classes of wastes. It permitted differentiation between four composted wastes and intrinsically different wastes (i.e., cattle manures, pig manures, and poultry manures) which could not be objectively regrouped. It also placed some very different types of waste (solid phase from pig slurry separation, pig manures, and composted pig mixtures) in the same class.