Contributions are a special type of government-imposed public income that are collected from citizens with purpose of financing the social security system. Various forms of social insurance have appeared in 14th century, but the notion of contributions was introduced to literature just at the end of 19th century. During their history, they were often compared with taxes and fees, although there are significant differences in contributions from these types of public revenues. In the Republic of Croatia mandatory social security contributions are contributions for pension insurance, for health insurance, for consequences of injuries at workplace and for employment. With those contributions, since the independence of the Republic of Croatia, contributions were collected for child support and for water contributions. Contributions can be collected at the expense of the employee or at the expense of the employer, the basis for calculating contributions is the gross salary of an employee. Contributions for pension insurance are now being paid from salaries, at the expense of the employee, while contributions for health insurance, labor injuries and employment are paid at the expense of the employer. Ways to collect contributions have changed through history. The contribution rate is prescribed by the law of a particular country and therefore contributions in the Republic of Croatia differ from other countries in the European union and the rest of the world. By analyzing the percentage of net social contributions in GDP of the EU member states, it has been established that there is a correlation between this percentage and the degree of state development.