Theme 1 of the BIOMASS project was established with the objective of developing the concept of ‘reference biospheres’ into a practical system for application to the assessment of the long term safety of repositories for radioactive waste. The outcome is the BIOMASS methodology developed through the construction of a number of example reference biospheres. The examples illustrate the use of the methodology and are also intended to be useful in their own right by acting as standard (or reference), stylized biospheres.