For creating new grouping criteria:

1.  Go to *Invoicing \> Configuration \> Management \> Invoicing
    Grouping Criteria*.
2.  Create or modify existing criteria, selecting fields belonging to
    "Sales Order" header model for grouping according them.
3.  Invoicing address and currency will always be applied with the
    selected ones.

For setting a different grouping criteria for a specific customer:

1.  Go to *Invoicing \> Customer \> Customers*.
2.  Open the desired customer.
3.  Go to *Invoicing* page.
4.  Set on "Sales Invoicing Grouping Criteria" the desired grouping
    criteria.

For setting a different default grouping criteria than the standard for
the whole company:

1.  Go to *Invoicing \> Configuration\> Settings*.
2.  Locate inside "Sales Order Invoicing" section, the field "Default
    Grouping Criteria".
3.  Introduce there the grouping criteria to be applied by default. If
    empty, the general default of invoicing address + currency + company
    will be applied.
