If you have a mortgage, student loans or a balance on your credit cards, you owe a debt. And if you do have debt, you’re in some good company – the U.S. federal government has tons of it.

As of June 4, 2018, the total outstanding debt owed by the federal government was $21,090,788,185,039.90, or $21.1 trillion. Yes that’s an astronomical number, but it’s not necessarily a bad thing; in fact, United States government debt is considered the safest in the world, according to Lawrence White, an economist at the NYU Stern School of Business.

“It is mostly an abstract concept, unlike, say, a personal student loan or auto loan or mortgage, where you have a personal obligation to repay the debt,” said White. “If you don’t repay, there are legal consequences that are going to be unpleasant. For an individual, the national debt has none of those particular characteristics. It is an obligation of the US, not an obligation of an individual.”

That doesn’t mean the national debt doesn’t affect you. If the US were to default on its debt, the interest rate on its debts would increase, which would be disastrous.

“That would mean our taxes would increase or other government spending would have to decrease,” said White. “It would throw financial markets into chaos.”

The federal government borrows money in the form of Treasuries (notes, bills and bonds; more on that later). Treasuries are a government’s debt obligation, and because they are backed by the credit and taxing power of a national government, they’re considered low-risk. Perhaps the biggest recent example of the use of borrowed money was the TARP program used to bail out the bank and auto industries in the wake of the 2008 financial crisis.

Who owns the national debt?

One of the biggest holders of national debt is the government itself. Federal agencies, like the Social Security Administration, the Office of Personnel Management Retirement, and Medicare own $5.7 trillion worth of the debt as of March 2018. This is called intragovernmental holdings. When an agency, like the Social Security Trust Fund, brings in more in tax revenue than it needs to spend, it buys US Treasuries.

Treasuries are the notes that hold value: there are Treasury notes, bills and bonds. The name refers to the time period a lender will hold on to it. Treasury notes are short-term, usually a few months; Treasury bills are medium-term, a few years; and Treasury bonds are long-term, more than a decade.

The remaining $15.4 trillion is held by the public – individuals and companies. This includes foreign governments. China is the largest foreign holder of American debt, holding around $1.19 trillion as of March 2018. Japan held $1.04 trillion as of March. It’s worth noting the US government also lends money to foreign governments.