Why is the dollar the world's reserve currency, and does it matter to you?

Central banks hold dollars, trade settles in dollars, and commodities are priced in dollars. The reserve status gives the dollar a structural bid and makes US policy everyone's problem.

Beginners: what does reserve status actually mean for a currency? Experienced members: when does it matter for your trades and when is it just trivia?

The DXY guide and how interest rates move currencies are good background.