You will be required to produce Baptism and Confirmation certificates and an ecclesiastical certificate of no impediment issued by your own bishop's office, as well as the appropriate civil documents if you wish to have a religious ceremony legally recognized by the Italian authorities. 
If a religious ceremony is to be performed by a Catholic priest, a separate civil ceremony will not be needed, as the priest will register the marriage with the civil authorities.
In case your civil ceremony was performed prior the religious ceremony you should show the original civil documents (the civil wedding certificate which states that you are legally married) to the Italian priest. 
If one of the Parties has been divorced, the Italian Catholic Church will not allow you to re-marry in a Church, unless the Rota (the only Institution legally able to officially annulled marriages) has previously annulled your wedding.


All foreign citizens who wish to legally marry in Italy must be able to provide the following documents:

• Passports
• Certificate of No Impediment
• Nulla Osta

Depending from their nationality, other documents might be necessary, like Apostille (a form of authentication issued to documents for use in foreigners countries) or Atto Notorio (Sworn Affidavit).
You will need two witnesses and one interpreter to translate your ceremony.

Citizens from different countries may need to provide different documents.

The following lists are given as an indication only.


For Russian citizens

In order to get married in Italy a Russian citizen needs a Nulla Osta which may be obtained by showing the the following documents to the Russian Embassy in Italy
• Both original Russian passports (internal and international); 
• Original Birth Certificate;

• If previously divorced/widowed, you need to show yourdivorce decree or death certificate 

• If documents bear different names, you have to show the document where we can see that you changed it officially.




For UK citizens

Each British national resident in the UK should provide the Italian city hall where they intend to marry the following documents:

• A Certificate of No Impediment – issued in the UK, legalised in the UK and then translated officially in Italy
• A bilingual Statutory Declaration legalised in the UK
• Passport

See more detailed information here.



For US citizens

US citizens planning to marry in Italy should present the following documents:
• US passport
• Birth certificate with Apostille and translated into Italian; it should show the names of both parents. 
• Evidence of termination of any previous marriage
• Atto notorio translated and with the Apostille seal. 
• Nulla osta issued by the Consular Section nearest you wedding destination, stating that “there are no impediments” to the marriage

See more detailed information here.