Equal Pay Act 1963
The Equal Pay Act on June 10, 1963 (effective June 11, 1964) made it illegal to pay women less than men for doing the same job strictly on the basis of their sex. This had been commonplace before. There had to be demonstrable differences in seniority, merit, the quality or quantity of work, or other considerations in order to merit different pay.
Two landmark court cases, Schultz v. Wheaton Glass Co. (1970), U.S. Court of Appeals for the Third Circuit and Corning Glass Works v. Brennan (1974), U.S. Supreme Court tightened and refined the language of the act.
In 1963, average wages for women were about 59% of the wages paid to men. In the UK, the gender pay gap derived from median hourly earnings (excluding overtime) in 2006 was 12.6 per cent using the median and 17.2 per cent using the mean. This means that women who work full time are paid on average 87.4 per cent of men's hourly earnings using the median and 82.8 per cent using the mean. The full-time gender pay gap decreased by 0.4 percentage points in 2006 using the median but increased by 0.1 percentage points using the mean. This was due to a higher growth in the earnings of men working full-time in the top decile. Because the mean can be distorted by a small number of high earners, who are predominantly men, the Office of National Statistics in the UK now recommends measuring the gender pay gap using the median value.
The part-time gender pay gap declined from 40.4 in April 2005 to 40.21 per cent in April 2006 using the median. Using the mean, the part-time gender pay gap was the same as it was in 2005. . American figures are slightly different. 
According to the UK government's Gender Pay Gap Fact Sheet:
The causes of the gender pay gap are complex and reflect to some extent current and historical choices. Key factors include: human capital differences: i.e. differences in educational levels and work experience; part-time working; travel patterns and occupational segregation. Other factors include: job grading practices, appraisal systems, and pay discrimination...Occupation segregation is one of the main causes of the gender pay gap. Women's employment is highly concentrated in certain occupations and those occupations which are female-dominated are often the lowest paid. In addition, women are still under-represented in the higher paid jobs within occupations - the "glass ceiling" effect. 
Gender Equality duty 2007
On April 6, 2007, the Gender Equality Duty came into effect in the United Kingdom. It was designed to be pro-active in tackling polices and practices that superficially appear gender neutral but can contribute to greater inequality.
The law deals with disadvantage to both genders generated by work patterns adopted by employers. Women are disadvantaged by systems that take no account of caring responsibilities, different patterns of working life, or greater vulnerability to domestic violence and sexual assault. Men are disadvantaged when workplaces do not recognize their family or childcare responsibilities or when family support services assume they are less involved in parenting, or when health services do not take into account their different needs. For example, research shows that men are less likely to visit their GP, and so may progress further into diseases such as lung cancer before being diagnosed.
The Gender Equality Duty also applies to transsexual men and women in terms of employment and training. The European Directive on equal treatment protects them from discrimination and harassment after the end of 2007.
To comply with UK law, all public bodies, and private or voluntary sector bodies who carry out public functions, must:
- Gather information on how their work affects women and men
- Consult all stakeholders
- Assess impact of policies and practices on both sexes
- Prioritise and set gender equality objectives
- Plan and take action to achieve objectives
- Publish a gender equality scheme
- Review progress every three years
The criticism has been leveled that this will increase bureaucracy, but the CBI Public Services Directorate has asked its members to look beyond bureaucratic processes to deliver better equality outcomes.
The element of proactivity in Gender Equality Duty means that it is now a statutory requirement for public organizations to consider the effects of its employment patterns on gender equality. In late 2007 a body called the Commission for Equality and Human Rights will take over responsibility from the current Equal Opportunities Commission for promoting and enforcing legislation on gender, disability and race.