When do you find out the gender?

Hello fellow mommies to be! 
This is my first and I am so ready to find out the gender of my little peanut. I have heard many different stories of when people got to find out the gender but most were from 25 years ago. At this day and age I know it's earlier on, so at what week do we find out if it's a boy or girl? And what's the earliest?