One of the aims of the HOPE project is to develop a method to assess healthiness and energy efficiency of buildings and strategies to optimise their performance towards health and energy efficiency. In this project, a building is defined "Healthy and Energy Efficient" if: it does not cause or aggravate illnesses of the building occupants; it assures a high level of comfort for the building occupants; it minimises the use of non-renewable energy taking into account available technology. Health and comfort performance criteria for buildings have been defined. They include a set of measurable parameters related to indoor air pollutants or physical characteristics of the indoor environment. Compliance with this set is expected to assure, with a high degree of confidence, the provision of acceptable performance of buildings and zones within them. Target values of the selected parameters have been set taking as reference the WHO air quality guidelines, when available. Health classification of buildings is based on health risk analysis from checklist data, if necessary integrated with measurements, and health- and comfort-related questionnaire data. To this purpose, health hazards have been divided into 3 groups and acute building-related symptoms are evaluated through the Building Symptom Index (BSI), a numeric indicator that considers the frequency of symptoms related to the Sick Building Syndrome (SBS) perceived by the occupants. In the end, the building is ranked according to the health status in one of 3 classes. Energy efficiency is evaluated by means of the energy index, i.e. the yearly total energy use per gross heated floor area, and the building is ranked accordingly. Combining the health and energy evaluation, the buildings are finally classified as optimal, medium, or low.