IntroductionWage differentiation may be caused by many reasons because wide range of factors are influencing e the situation with wage rate sat all labour markets. If the occurring wage inequalities between men and women result from differences in their education, job experience, the position held, professional group, workplace etc. - these inequalities are thus justified, stemming from different socio-professional and demographic characteristics. However, when the pay gap disfavoring women occurs in situation of very similar socioprofessional and demographic characteristics of men and women - it may be stated that it is wage discrimination against women.The legislation and rules in force in Poland ensure formally the equality of men and women at the labor market. Regulations regarding the elimination of all forms of discrimination against women at the labor market1 are included in the United Nations Convention and the Conventions of International Labour Organization2. The European Union, by means of its policy of equal opportunities in Member States, implemented number of directives, recommendations and programs concerning the elimination of discrimination against women3. Among the national laws, the Constitution of the Republic of Poland should be enumerated, which states that a woman and man have in particular equal rights to education, employment, promotion, equal wages for work of equal value...4. The principle of equal treatment of men and women in the matters of employment, remuneration and promotions, as well as access to training5 is covered in the Labor Code of Poland.The analysis of statistical data, as well as the result of numerous studies on wage formation show that in Poland there is gender pay gap unfavorable for women. If - in spite of legislation and rules in force - such differentiation results from wage discrimination of women, it would mean there is market in Poland and hence both supply and demand for such discrimination. We formulate research hypothesis that lasting wage discrimination of women exists in Poland. It results mainly from commonly shared values, norms and traditional roles in the society, and this discrimination is accepted by vast majority in the society6. Therefore, the key aim of this paper is the assessment of wage formation for men and women in Poland, taking into account the situations when men and women have very similar socio-professional and demographic situations, and also the presentation of most widely spread theories of wage discrimination against women along with their verification on the study case of Polish labor market. For our research we have chosen the time period from 1991 till 2015, and since this is quarter of century under study, this would allow us determine the developed regularities, therefore, we were also able to verify the formulated above research hypothesis7.1.Wage discrimination of women in selected economic and sociological theoriesNumerous economic and sociological theories have been dedicated to the phenomenon and causes of discrimination of women on the labor market. Presenting all these theories in this paper is neither possible nor reasonable8. Therefore, only such theories were selected which seem to be of particular usefulness, from the viewpoint of wage discrimination of women, and for which there is possibility of partial verification in the aspect of the research hypothesis and the aim of this paper9.In economic theories the causes of wage discrimination of women are considered in the approach of perfect and imperfect labor market10. Among the economic theories based on the assumptions of perfect labor market, it is worth to consider presenting the taste for discrimination (personal prejudice) theory, Human Capital Theory and the information cost theory. These theories, despite perfect labor market assumptions, may also refer to the economic reality (Kalinowska-Nawrotek, 2005, p. 13). …