David wrote:

How can I prevent a user minimising the workbook?

Preventing it is difficult but you can immediately reverse it.

Private Sub Workbook_WindowResize(ByVal Wn As Window)
If Wn.WindowState = xlMinimized Then Wn.WindowState = xlMaximized
End Sub


I would also like to prevent them using the restore or
close buttons (I have a close option on a custom menu bar).

If what you want to do is to keep it maximized and open, try:

Global gbOkToClose As Boolean

Private Sub Workbook_WindowResize(ByVal Wn As Window)
Wn.WindowState = xlMaximized
End Sub

Private Sub Workbook_BeforeClose(Cancel As Boolean)
If gbOkToClose = False Then Cancel = True
End Sub

Obviously, you need to set gbOkToClose to True in your close button

--
Steve Garman