Diversity of representation is important for the democratic principles of equality, effectiveness, fairness, justice and legitimacy. However, the lack of good quality and consistently defined data for most protected characteristics considerably hampers the monitoring of the diversity of political representation in Britain. The aim of this report is to assess the quality of the available data on the diversity of candidates and elected officials at UK, national and local election levels and to identify where there are data gaps and limitations. The report draws together the best currently available data on the protected characteristics of candidates standing in the 2016 and 2017 elections in Great Britain. The report also sets out recommendations for improving the monitoring of diversity of political representation. Few data are available for most of the protected characteristics defined in the Equality Act 2010, and what is available is often drawn from reduced sample sizes. This reveals a fragmented picture with many gaps, making it difficult to assess confidently the diversity of political representation in Britain. Much of the current evidence relies on observation or self-reporting in surveys, and low response rates to those questions highlights the challenge of collecting this sort of information. However, the data that are available indicate that elected representatives in Great Britain remain unrepresentative of the population in their socio-demographic characteristics. Our assessment of diversity is drawn from information available on the diversity of candidates and elected representatives in the House of Commons, the Scottish Parliament, the National Assembly for Wales and local elections. The focus is on six out of the nine protected characteristics listed in the Equality Act 2010 for which data were available: age, disability, race, religion or belief, sex and sexual orientation. No data were available for gender reassignment. Section 106 of EA 2010 places a statutory obligation on political parties to collect and publish information relating to the protected characteristics of candidates for the UK Parliamentary, European, National Assembly for Wales and Scottish Parliament elections. However, section 106 has not been brought into force.