What does the spouse of an Italian citizen need in order to stay in the Schengen area for more than 90 days?

The reason for the delay in answering this question is that it was not known whether European freedom of movement rights would apply, because a country can treat its own citizens' family members more restrictively. Countries that do this include the United Kingdom, the Netherlands, and Germany.

Apparently, Italy does not make a distinction between the non-EU family members of Italian citizens and the non-EU family members of non-Italian EU citizens. Or, at least, they do not treat family members of Italian citizens more restrictively than they do those of other EU citizens.

The Italian implementation of the freedom of movement directive applies its provisions to the family members of Italian citizens, where its provisions are less restrictive than those otherwise in force:

Art. 23.

Applicabilita' ai soggetti non aventi la cittadinanza italiana che siano familiari di cittadini italiani

1. Le disposizioni del presente decreto legislativo, se piu' favorevoli, si applicano ai familiari di cittadini italiani non aventi la cittadinanza italiana.

Translation:

Article 23

Applicability to those, not having Italian citizenship, who are family of Italian citizens

1. The provisions of the present legislative decree, where more favorable, apply to the family members of Italian citizens who do not have Italian citizenship.

Source: http://www.esteri.it/mae/normative/normativa_consolare/visti/d_lgs_30_2007.pdf

See also http://www.esteri.it/mae/en/ministero/servizi/sportello_info/domandefrequenti/sezione_visti_entrare_in_italia.html, which includes the following question and answer:

What do I need in order to apply for a visa as a family member of an Italian citizen?

The family members of EU and EEA citizens can apply for visas in accordance with Italian legislative decree 30/2007, art. 2.

The required documentation includes:

• Visa application (click here)
• A recent photograph
• A valid travel document with expiration date of at least 3 months beyond that of the visa requested
• A marriage certificate or other adequate documentation demonstrating familial relationship
• In the case of minors, written consent to the issuance of the visa by the other parent

For more information see the Visa Database.

This clearly implies that you can benefit from the EU freedom of movement provisions.

As a US citizen, your husband does not need a visa to enter Italy, but he does need a residence permit to stay in any EU country for more than 90 days. He should therefore apply for one in Italy if you plan to stay for more than 90 days. However, if you are traveling around Europe, you may not be staying for more than 90 consecutive days in any one country, so it may be okay if he doesn't apply for the residence permit. Certainly, the way it is set up in France, it doesn't make sense to apply for one if you're just going to be there for 4 or 6 months.

If you decide to undertake the formalities for a stay of more than three months, you can refer to the information at http://www.poliziadistato.it/articolo/10930-European_Union_citizens:

EU nationals who whish to stay in Italy for a period exceeding three months should register with the Anagrafe (Register Office) of the municipality of residence.

The following documents must be included with your application:

a) if employed or self-employed: evidence of your activity;

b) if studying, training or staying for reasons other than work: proof of maintenance, calculated according to the Italian minimum annual social security allowance in relation to the number of dependent family members (a self-certification is accepted); proof of sickness insurance to cover health care costs; evidence of your university course (only if studying);

c) if family member of an EU citizen, national of another member country without autonomous right of residence: proof that you have a family link with the EU citizen or that you are a dependent relative (self-certification is accepted).

You will receive a receipt certifying that you have applied for registration to Anagrafe.

Family members without autonomous right of residence must provide:

• valid passport or any other equivalent travel document bearing an entry visa, if required;
• proof of family relationship with the EU citizen and, if required, proof of being a dependent on the EU citizen;
• receipt certifying that the EU citizen applied for registration to Anagrafe.

EU citizens who applied for a residence permit before April 11, 2007 can register with the Anagrafe submitting the receipt issued by the Police Headquarters (Questura) or the Post Office (Poste Italiane) and self-certification of the requirements of the new legislation.