This chapter describes the nature of the two bioeconomy resources: biomass and biological knowledge. Biomass is primarily produced in the process of photosynthesis, which is described in the first part of this section. In this process, CO2 and water are converted into carbohydrates by autotrophic organisms using energy from sunlight. How well plants perform in this process of converting light energy into chemical energy through the incorporation of carbon (C) into their substance depends on many factors, including climate and soil properties. The resulting biomass can be characterized by its origin (plants, animals or microorganisms), the sectors in which it is produced, its main components or its physical state. The third part of the chapter describes how these biomass characteristics can be improved or designed through breeding. It explains the principles of breeding, green biotechnology, genetic engineering and synthetic biology. These are all technologies that are applied when biological knowledge is used. Biological knowledge is described in the fourth part of the chapter. It is the combination of biological data and the interpretation of their meaning. Elements of biological knowledge include ‘omics’ for learning from large data sets, conventional and molecular biotechnologies, and bionic and biointelligence approaches. Practical examples for so-called nature-based solutions, that is, solutions inspired and supported by nature, are described in the fifth section. The chapter concludes with a global view on primary biomass production and land resources and how to assess biomass availability.