In recent years, both in the European Union and in the world, there has been intense development of organic agriculture, whose aim is to produce high-quality crops and healthy food while maintaining the biological balance of agroecosystems. An alternative to chemical fertilizers are products of natural origin, organic fertilizers, biofertilizers or natural growth bio-stimulants, which increase plant growth, yielding and resistance to pathogens and pests, and improve soil fertility, productivity and biodiversity. The chapter examines the role of biofertilizers and consortia of microorganisms to improve the effectiveness of organic fertilization, before moving on to consider the use of animal excrement, including manures, slurry and guano. The chapter considers the use of products or by-products of both animal and plant origin as fertilizers, before addressing the contributions of composts and biochar.