Fifteen homelessness experts were asked to complete a questionnaire on the enumeration of homeless people, and the estimation of the homeless population in the 2011 national level censuses that took place across the European Union. The experts were requested to draw upon their own knowledge, collect and review relevant material that detailed census methodologies, which were related to homelessness. They also conducted interviews with staff in census offices and with homelessness NGOs and other agencies that had a particular interest in the enumeration or estimation of the number of homeless people. Questionnaires were distributed to experts in the Czech Republic, Denmark, France, Germany, Hungary, Ireland, Italy, Lithuania, the Netherlands, Poland, Portugal, Slovenia, Sweden, Spain and the UK. Some EU member states have relatively rich data on homelessness. These countries all tend to define people living rough and in emergency shelters or accommodation as being homeless. However, people in precarious or unfit accommodation, or who are concealed or ‘hidden’ in households, for example two families in housing designed for a single person or one family, may be regarded as homeless in one country but not viewed as homeless in another. This means there is inconsistency in the size and nature of the population that is defined as homeless, and therefore in the population which is counted or estimated as being the ‘homeless’ population across different countries.