`querySelector` and `querySelectorAll` are both methods used to select elements in the Document Object Model (DOM).
The main difference between these two methods is:
`querySelector`: This method returns the first element that matches a specified CSS selector(s) in the document. If more than one element matches the selector, only the first matching element will be returned.
`querySelectorAll`: This method returns all elements in the document that match a specified CSS selector(s), not just the first one. The result is a static NodeList.
In short, if you want to select only the first matching element, you would use `querySelector`. If you want to select all matching elements, you would use `querySelectorAll`.