How to duplicate a whole line in Vim?

Question

How do I duplicate a whole line in Vim in a similar way to Ctrl+D in IntelliJ IDEA/ Resharper or Ctrl+Alt+&

Answer 1

1 gotcha: when you use "p" to put the line, it puts it after the line your cursor is on, so if you want to add the line after the line you're yanking, don't move the cursor down a line before putting the new line.