As a result of the increasing burden on the environment and the scarcity of natural resources, we need to find new ways of supplying a growing population with products for daily life. In a bio-based economy we want to produce bioplastics, biochemicals and biofuels from plant biomass. Cellulose is a renewable resource, and can provide the starting point for many products that can satisfy the increasing demand for sustainable and biocompatible products. Cellulose serves as a strengthening component in plants, and its structure is therefore resilient and complex. We need to use certain enzymes, known collectively as cellulases, which are produced by other microorganisms, such as bacteria and filamentous fungi, to degrade cellulose into glucose, which can serve as an energy source. In the laboratory, these microorganisms are grown under harsh conditions, where the production of enzymes takes place in closed tanks containing nutrients, which are stirred while air is supplied. The aim is to produce large amounts of enzymes within a few days, so that they can be added to cellulose to break down the cellulose into glucose as quickly as possible. During the course of this work, I studied the structure of cellulose during enzymatic hydrolysis with the aim of expanding our knowledge on the reason why cellulose is so difficult to break down and, in the longer perspective, to improve enzymatic hydrolysis.