Biomass includes a wide variety of raw materials diverse in morphological, anatomical, structural, chemical and physical properties that vary significantly within and between the different biomass raw materials. Understanding these properties is essential and depending on the application, differences in biomass characteristics may be critical for their final performance. Biomass can provide food, materials, chemicals and/or energy, using various transformation processes such as combustion, gasification, fermentation, liquefaction, pyrolysis. To increase the share of biomass in economy, the most essential features related to biomass use are: (1) to enlarge and improve the basic knowledge on biomass availability, composition and properties; (2) to apply this knowledge for best available technology in its conversion. Each biomass resource has different characteristics that require appropriate conversion technologies for efficient utilization. The route to products depends on the biomass characteristics. Therefore, an important step in the conversion systems is the evaluation of the biomass availability and its morphological, chemical, physical, and energetic characteristics. The identification of (1) anatomical characteristics; (2) chemical composition (cellulose, lignin, hemicelluloses, extractives and inorganic content); (3) chemical characteristics (carbon, hydrogen, oxygen, nitrogen, sulfur, and other elements content); (4) physical parameters (density, moisture); (5) proximate analysis data (fixed carbon, volatile compounds and ash content); and (6) energetic parameters (higher heat value, lower heat value) of biomass is the initial and most important step during the investigation and application as a raw material. These properties determine biomass quality and quantity, potential applications and environmental problems related to its use for particular purposes, but also can be used for characterization and future advanced sustainable exploitation of biomass as a large-scale resource in economy, including collection, transportation, storage, upgrading, digestion, fermentation, gasification, liquefaction, pyrolysis and combustion. In conclusion, in order to understand the biomass potential, it is of vital importance to gain better knowledge of biomass composition and properties, which may provide decisive factors not only for its applicability, but also for the economic practicability and environmental security of many processes involving biomass.