Equality between women and men is a fundamental principle of European Union (EU) law that applies to all aspects of social life. The EU has adopted a two-pronged approach to gender equality, combining specific measures with gender mainstreaming. Policies on gender equality have been drawn up since the creation of the European Economic Community (EEC) in 1957, with the Treaty of Rome. Following the establishment of the founding treaty, this basic principle was gradually clarified and developed by several Council directives, which dealt mostly with economic perspectives including pay, employment, health and safety, maternity and parental leave, as well as other issues pertinent to work–life balance. None of these legal measures, however, dealt specifically with the principle of gender equality. It was only in 1996 that the European Commission itself took a dual approach to gender equality by both implementing gender mainstreaming and initiating specific measures. In February 1996, the Commission adopted a Communication on Mainstreaming in relation to policies at Community level: ‘The principle of “gender mainstreaming” consists of taking systematic account of the differences between the conditions, situations and needs of women and men in all Community policies and actions. This global, horizontal approach requires the mobilisation of all policies’ (European Commission, 1996). The principle of gender equality has been strengthened, notably since the 1997 Treaty of Amsterdam, by including the principle of gender mainstreaming in the EU’s founding text. Subsequently, the introduction of the Lisbon Treaty in 2009 marked a turning point as it directly addressed the principle of gender equality, and the policies to support it, as a central element of EU policy. It emphasised the importance of eliminating all types of discrimination, including those based on sex, through the Charter of Fundamental Rights of the European Union (2000), while a declaration in relation to Article 3 of the Lisbon Treaty gave renewed attention to how gender-based violence in the EU threatened the integrity and dignity of women and men. The Council Conclusions on the ‘review of the implementation by the Member States and the EU institutions of the Beijing Platform for Action: Indicators in respect of Institutional Mechanisms’ (1) (2006) emphasised that a formal commitment and formal structures for gender mainstreaming are not sufficient and that practical action in all relevant areas is needed. It reiterated and reaffirmed its previous position and urged all Member States and the Commission to improve and strengthen the development and regular use of mainstreaming methods, particularly gender budgeting and gender impact assessment (GIA), when drafting legislation, policies, programmes and projects. In this framework, gender impact assessment is the basic method for the governmental structures to use for gender mainstreaming. As part of Indicator 3 on Gender Mainstreaming, introduced by the Finnish Presidency of the Council of the European Union (2) in 2006, it defines the aspects to measure as the progress of Member States in the area of institutional mechanisms and gender mainstreaming. The report on institutional mechanisms for gender equality developed by the Finnish Presidency of the Council of the EU in 2006 provides information on gender impact assessment in law drafting as well as in drafting policy programmes, action plans and projects. The gender impact assessment is one of the methods for gender mainstreaming. It should be used in the very early stage of any policymaking, i.e. when designing it. The GIA is an ex ante assessment1 and this implies the integration of a gender analysis at the ‘define’ stage of the policy cycle. The aim is to achieve a significant impact not only on the policy design but also on its planning, in order to ensure adequate equality outcomes. Finally, it is important to highlight that the application of gender impact assessment is a learning process, since there is no common regulation, model or development within the public administration at European level. It is not intended, therefore, that this guide be used as a replacement for existing support tools. Nor is it intended to serve as ‘hard instructions’ to be followed to the letter. The intention is that it will perform a timely function to encourage and enable reflection on one’s current practice in this field, to provide suggestions and hints for particular challenges, and to inspire with new ideas and ways of adapting existing methods. These guidelines build upon the information collected from the project on institutional mechanisms for gender mainstreaming, commissioned by EIGE in 2012 and further processed in 2014. They also integrate the opinions and experiences of Member States’ representatives in EIGE’s Thematic Network on Gender Training as well as those of relevant gender equality experts.