Review summarizes the research on the biomass conversion for production of chemicals and an overview on recent activities of our research group on isolation of substances from biomass using sub- and supercritical water. Herein, hydrothermal processing of biomass waste represents an alternative approach to upswing the productivity chemicals, basic chemicals for synthesis and plant-based pharmaceutical compounds. The processing concepts to obtain products and product classes based on biological raw materials in gaseous, liquid, or solid state are presented. Subcritical water is discussed as a highly reactive media to enhance extraction affinity of value added compounds, such as proteins and amino acids, essential oils, oils and fatty acids, carbohydrates and phenolic compounds from natural sources.