National Insurance (NI) is a system of social security contributions in the United Kingdom that is used to fund state benefits such as State Pension, unemployment benefits, and healthcare. National Insurance contributions are paid by employees, self-employed individuals, and employers, and the amount of contributions that an individual is required to pay depends on their income and employment status.

National Insurance contributions are collected by HM Revenue and Customs (HMRC) and are recorded against an individual's National Insurance number, which is a unique personal identification number. National Insurance contributions are used to build up an individual's entitlement to certain state benefits, such as the State Pension, and they are also used to fund the National Health Service (NHS).

In the UK, National Insurance contributions are divided into different classes, and different rules apply to each class. For example, Class 1 contributions are paid by employees and their employers, and Class 2 and Class 4 contributions are paid by self-employed individuals.

If you are working or self-employed in the UK, it is important to understand your National Insurance obligations and to ensure that you are paying the correct amount of contributions. If you have any questions about National Insurance or need help with your contributions, you can contact HMRC for assistance.