Textbox - pressing enter - avoid page load - instead perform a function in code behind

Hi All,
Happy New Year.
When pressing enter in a textbox, the page reloads.
But the desired behaviour in my application (and I am sure this is a common requirement) is that instead an action in the code behind is executed, in my case, the same action as if the user would press a button next to the text box.
How can this be achived? I imagine some sort of association of the text box to the button, or some sort of onpressenter = button_click().
Any solutions out there to this common issue?
I use csharp by the way.
Cheers,
D

...