Source: Wikipedia

The Italian Language, La lingua italiana.

Italian is a Romance language spoken by about 70 million people, most of whom live in Italy. Standard Italian is based on Tuscan dialects and is somewhat intermediate between the languages of Southern Italy and the Gallo-Romance languages of the North. The long-established Tuscan standard has, over the last few decades, been slightly influenced by the variety of Italian spoken in Milan, the economic center of Italy. Italian has double (or long) consonants, like Latin (but unlike most modern Romance languages, e.g., French and Spanish). As in most Romance languages (with the notable exception of French), stress is distinctive.
History.

The history of the Italian language is quite complex but the modern standard of the language was largely shaped by relatively recent events. The earliest surviving texts which can definitely be called Italian (as opposed to its predecessor Vulgar Latin) are legal formulae from the region of Benevento dating from A.D. 960-963. Italian was first formalized in the 14th century through the works of Dante Alighieri, who mixed southern Italian dialects, especially Sicilian, with his native Tuscan in his epic poems known collectively as the Commedia, to which Boccaccio later affixed the title Divina. Dante’s much-loved works were read throughout Italy and his written dialect became the canonical standard that others could all understand. Dante is still credited with standardizing the Italian language.

Italian has always had a distinctive dialect for each city, since the cities were up until recently city-states. Italians generally believe that the best spoken Italian is lingua toscana in bocca romana - ‘the Tuscan tongue, in a Roman mouth’ (Tuscan dialects spoken with Roman inflection). The Romans are known for speaking clearly and distinctly, while the Tuscan dialect (supposedly derived from Etruscan and Oscan), is the closest existing dialect to Dante’s now-standard Italian.

In contrast to the dialects of northern Italy, the older southern Italian dialects were largely untouched by the Franco-Occitan influences introduced to Italy, mainly by bards from France, during the middle ages. (See La Spezia-Rimini Line.) The economic might and relative advanced development of Tuscany at the time (late middle ages), gave its dialect weight, though Venetian remained widespread in medieval Italian commercial life. Also, the increasing cultural relevance of Florence during the periods of ‘Umanesimo’ and Rinascimento (Renaissance) made its vulgare (dialect) a standard in the arts.
Classification

Italian is a member of the Italo-Dalmatian group of languages, which is part of the Italo-Western grouping of the Romance languages, which are a subgroup of the Italic branch of Indo-European.
Geographic distribution

Italian is the official language of Italy and San Marino, and is an official language in Ticino and Grigioni cantons of Switzerland. It is also the second official language in Vatican City and in some areas of Istria in Slovenia and Croatia with an Italian minority. It is widely used by immigrant groups in Luxembourg, Germany, Belgium, the United States, Canada, Venezuela, Brazil, Argentina, and Australia, and is also spoken in neighbouring Albania. It is spoken, to a much lesser extent, in parts of Africa formerly under Italian rule such as Somalia, Libya and Eritrea. It is also widely known and taught in Monaco and in the neighbouring island of Malta and served as an official language of the country until English was enshrined in the 1934 Constitution.
Official status

Italian is an official language of Italy, San Marino, Switzerland and Vatican City. It is also an official language in the Istria County (Croatia) and municipalities of Koper, Piran and Izola (Slovenia).
Dialects

The dialects of Italian identified by the Ethnologue are Tuscan, Piemontese, Abruzzese, Pugliese (Apulian), Umbrian, Laziale, Central Marchigiano, Cicolano-Reatino-Aquilano, and Molisan. Other dialects are Milanese, Brescian, Bergamasc, Modenese, Bolognese, Sicilian and so on, essentially one per city.

Also the Corsican language has strong similarities to Italian and most linguists consider it as a Tuscany dialect, the closest to modern Italian.

Many of the so-called dialects of Italian spoken around the country are different enough from standard Italian to be considered separate languages by most linguists and some speakers themselves. Thus a distinction can be made between “dialects of (standard) Italian” and “dialects (or languages) of Italy”.

A link to an Italian site with translation features between Italian dialects and Italian:
Cultural acceptance of dialects

Dialects are generally not used for general communication, e.g. on TV, but are limited to groups of people who can actually speak them and to informal contexts. Speaking dialect is often shunned upon in Italy as it is a sign of lacking education. Younger generations, especially those under 25, speak almost exclusively standard Italian in all situations, usually with a slight local accent.

Dialects have their share of enthusiasts, but this is a small niche of the population. The promotion of dialects by some political forces as the Lega Nord has possibly damaged rather than promoted their status.

Dialects are often used in movies to provide comic relief or to produce stereotypes: northern dialects can be connected to greedy merchants; a Roman accent is associated with arrogant, simple-minded bullies; Neapolitan reminds of dishonest, cunning slackers, and, even in Italy, Sicilian is often associated with the mafia. However, many screenwriters also explore the more expressive and spontaneous features of a dialect, often to challenge the common cliches and present a richer, less explored reality.
Grammar

see Italian grammar.
Dictionaries

The classic Italian dictionary is Zingarelli.
Many Italian/English dictionaries are available.