The assessment of biomass and carbon in tropical forests is gaining more and more attention. This is due to their role of providing livelihoods to more than a billion people, their vast timber resources, their provision of shelter to more than half of the known plant and animal species, as well as to the role of tropical forests in the global climate system and climate change. They represent the biggest terrestrial carbon pool and cycle more water than any other biome. The high uncertainty about the amount of biomass and carbon stored in tropical forests and their decrease due to anthropogenic deforestation and forest degradation renders more detailed knowledge necessary to better understand the real importance of this biome. In this chapter we are going to introduce different techniques for the assessment of biomass and its translation into carbon that is stored in tropical forests to describe the status quo at a given point in time. The calculation of changes over time requires assessments on at least two occasions and subsequent application of statistical methods which are described in other chapters of this book. We focus on the five biomass pools as stipulated by the Intergovernmental Panel on Climate Change (IPCC), which are aboveground and belowground biomass and deadwood, litter, and soil organic matter. For each pool the specific requirements for assessing biomass are explained and the single-assessment steps are described. Besides this, we give an overview on commonly used reference values from the literature for the case that a physical assessment of a certain pool is not feasible.