• valid identity card, electronic residence permit (eAT) or passport with current confirmation of registration
• Electronic insurance confirmation as an eVB code (available from your car insurance company)
• Registration certificate part II (vehicle registration document)
• Registration certificate part I (vehicle registration document) or deregistration certificate
• If no registration certificates have been issued yet, foreign registration documents and original purchase contract, if applicable
• Classic car appraisal
• Certificate of inspection of the main vehicle inspection (TÜV)
• for the payment of vehicle tax, an original SEPA combined mandate for direct debit
  (If the tax is to be paid not by the owner himself but by a so-called willing third party, a copy of the willing third party's identity card must be submitted.)
• Appointment confirmation

• Original power of attorney with a legible color copy of the principal's ID card
• Original ID of the authorized representative

Additionally for companies or associations:

• Proof of legal authority (e.g., an extract from the commercial register or an extract from the association register)

Additionally, when applying for red license plates for classic cars:

• Current certificate of good conduct (not older than 3 months) feature O for official purposes, to be applied for at the registration authority