I have set up a subform with a command button to open a 'notes' form. I want it to only pick up data which is linked to the main forms record. I have set up a relationship between 2 matching fields but it still shows all records rather than just 1 specific one.

Help!!

If I understand you correctly, it would probably be easier, and more beneficial later, to use queries to link/combine the information. And then use a subform based on that query in your main form if you need it there.

Look in help at the options available for the OpenForm Method. You'll see how to use a filter or Where clause to restrict the data shown by the notes form.