Humic acids (HA) make up an important component of soil humus related to the maintenance of soil water-holding capacity, stabilization of soil structure and fertility and vital activity of soil micro-organisms, plants and animals. Additionally, obtaining humic substances (HS) from vermicompost has shown to be a promising alternative for large scale use in agriculture. Humic substances (HS) are also major components of natural organic matter (NOM) in soil and water as well as in geological organic deposits. This book includes chapters on vermicompost-derived liquid humus in low-input and small-scale farming; the production of liquid organic fertilizers enriched with humic substances from olive mill wastes; mechanisms of protective action of the HUMI preparation on wheat plant response to toxic ions; the application of surface-enhanced Raman scattering and fluorescence spectroscopy on silver plasmonic nanoparticles as innovative techniques to study humic substances; the complexation of metal ions with humus substances in soils and water and the final chapter examines the natural organic matter in drinking water.