When is it required to have a National Insurance number?

National Insurance is essentially the UK's social security system, and it's all about contributing towards things like your state pension and access to certain benefits. The whole system is designed to track your contributions throughout your working life. So, when you start working, you need a National Insurance number so that Her Majesty's Revenue and Customs, or HMRC, can properly record your contributions and ensure you get what you're entitled to later on. It's a unique identifier, like a social security number in other countries, and it stays with you for life. You don't need it for things like using public transport; that's just a regular ticket. And while you continue to pay National Insurance after you start working, the *requirement* to *have* the number kicks in right at the beginning, when you're first employed. Think of it as your official entry pass into the UK's contribution-based welfare system.