As has been explained elsewhere, a large proportion of Italian surnames are patronymics, that is, surnames derived from given names (the father's name). Among male names, Giovanni is the one that has generated the greatest variety of Italian surnames. Giovanni (John) is a name that comes from the Hebrew Yohanan, meaning "faithful to God", and which passed from Hebrew into other languages. John is also the name of two of the most venerated saints in Catholicism: Saint John the Evangelist and Saint John the Baptist.

The cult of these two saints was strong from the dawn of Christianity, but grew ever more established in the Middle Ages, accompanied by numerous dialect variations of the name. It should be recalled that, in many cases, dialect was the only language spoken by the population. Ianni is a version of Gianni (a contraction of Giovanni), very common in the dialects of southern Italy, and is also found as a surname: Ianne, Ianni.

With the addition of suffixes —which lend a familiar or affectionate nuance— numerous variants arose:

• Ianna, Iannella, Iannelli, Iannello
• Iannicelli, Iannicello, Iannielli, Ianniello
• Iannilli, Iannillo
• Iannacci, Iannaccio, Iannacco, Iannaco
• Iannetta, Iannetti, Iannotti, Iannone, Iannoni
• Iannucci, Iannuccilli, Iannuccillo, Iannuccio
• Iannuzzelli, Iannuzzi, Iannuzzo
• Iannarelli

The letter J corresponds to what is called the "i lunga" (long i) in Italian, but it fell out of use during the 20th century, although it survives in many surnames. Some examples are:

• Janne, Janni, Jannelli, Jannello, Janniello
• Jannuzzi, Jannuzzo, Jannarelli
• Jannacci, Jannaccio, Jannacco, Jannaco

All of them derive from the name Giovanni. For their part, Ianes and Janes are surnames typical of Trentino, probably originating in a dialect form of the name Johannes. Ianich, by contrast, is a variant proper to the Udine area.

Finally, Iannopollo is a surname characteristic of Reggio Calabria which probably derives from the Italianization of the Greek surname Ianapoulos or Iannopulos, whose meaning is likewise "son of Giovanni (John)".