Fossil fuel reserves depletion, global warming, unrelenting population growth, and costly and problematic waste recycling call for renewable resources of energy and consumer products. As an alternative to the 100 % oil economy, production processes based on biomass can be developed. Huge amounts of lignocellulosic wastes are yearly produced all around the world. They include agricultural residues, food farming wastes, "green-grocer's wastes," tree pruning residues, and organic and paper fraction of urban solid wastes. The common ways currently adopted for disposal of these wastes present environmental and economic disadvantages. As an alternative, processes for adding value to wastes producing high added products should be developed, that is the upgrading concept: adding value to wastes by production of a product with desired reproducible properties, having economic and ecological advantages. A wide range of high added value products, such as enzymes, biofuels, organic acids, biopolymers, bioelectricity, and molecules for food and pharmaceutical industries, can be obtained by upgrading solid wastes. The most recent advancements of their production by biotechnological processes are overviewed in this manuscript.