Is it possible to link to javascript held within another file, in a similar way to linking to external CSS?

I understand that the 'calls must be in place in the html etc', but it would make things much easier if I could have one external 'common JavaScript file'.

If it is possible could someone give me an example of the correct method of doing this - eg and example for a link to a CSS file would be this:

What is the equivilent for JS? - If possible.
<style type="text/css">
<link rel="stylesheet" href="../css/standardstyles.css">

Cheers in advance