What the paper actually says
A certificate of no impediment says only this: on the day it was written, nothing in the Italian records barred you from marrying. It comes from the comune where you are on the civil register. Learning how to apostille a Certificate of No Impediment matters because a registrar abroad will not take a bare Italian sheet with no stamp on it.
An apostille is the stamp that fixes that. It is one certificate proving the signature on your paper belongs to a real officer. To apostille a Certificate of No Impediment in Bari you need the paper in hand first, signed by the registrar, with your details spelled the way your passport spells them.
The desk that stamps it
Because a town hall wrote it, this is an administrative paper, and administrative papers go to the Prefettura (Prefecture). You apostille a Certificate of No Impediment in Italy at the Prefettura of the province in which that town hall sits, so a paper from a village near Bari is handled here. A judgment from a court would take the other road, to the Procura della Repubblica.
Cost, and why speed matters
The apostille cost for a Certificate of No Impediment in Bari is set by law: a €16 tax stamp per document, with some papers exempt. Money is not the pressure here; time is. This paper has a short shelf life, the queue length varies, and a wedding date does not move, so book the errand early and keep the two steps close together.
What registrars abroad ask for
Requests arrive under many names: a nulla osta, a free-status paper, or the legalisation of a Certificate of No Impediment in Bari, which is the older word for the same job. Italy has belonged to the Hague Convention since 1978, so member states accept the single stamp. For a wedding outside that group, write to the registrar and ask what they need.
Translation, and the details people miss
The stamp does not translate a word. A registrar who works in another language will want a sworn translation, made by a translator who signs an asseverazione, a formal statement of accuracy, before an Italian court. Ask whether they want the stamp rendered too, and check they accept a translation done in Italy rather than locally.