Just open OrderF to a new record and set the focus to the Subform.

    DoCmd.OpenForm "OrderF", , , , acFormAdd
    Forms!OrderF!OrderDetailF.SetFocus

John

I would start by saying that adding unnecessary complexity to your database will only make it more challenging for you in the future if/when things don't work due to future changes in your database.  If you're going to open a Form to select the Customer, why not just use the database the way it is?  (Rhetorical question)

You could just as easily add a customer combo to your main form with a button that only appears after a customer is selected instead of having a Popup/Modal Form.  (Popup/Modal Forms can be challenging to work with)

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To answer your question:

The VBA for the Button on your main Form will be:  DoCmd.OpenForm "Popup/Modal Form"

Once your Popup Modal Form is Open... you'll have the combo box setup the same as the one in the Order Form.  

Once the user has selected the customer, they should have 2 buttons... a Cancel Button, which will just close the form...

Then an "Order" button which will do the following:
1. Open the Order Form, the VBA will look like this: DoCmd.OpenForm "OrderF", ,"CustomerID="CustomerID, acFormAdd
2. DoCmd.Close acForm, Me

You might have a problem doing this this way as I don't know if VBA can open the Order Form with a Popup/Modal Form open.

-Raymond

Thaks folks. About an hour after I sent this I realized I did not need to get this complicated. But, you did show how to reference the sub form. And that I thank you for.

Value From a Form
Value From Subform