Giacomo, like Giovanni, Domenico, Antonio, Pietro and Marco, belongs to the group of names of Christian tradition that gave rise to numerous surnames. Giacomo, Giacobo, Giacopo and Giacobbe are, in origin, the same name. It is a male given name, corresponding to the English James and Jacob.

The name Jacopo, derived from the Hebrew Giacobbe, together with the Greco-Byzantine variant Giacomo (very widespread during the Middle Ages), gave rise to a great variety of surnames of religious inspiration. Ya'āgob is the name of the patriarch Jacob in the Old Testament, and of the apostles James the Greater and James the Less in the New Testament. The Hebrew name, in turn, derives from Yah, an abbreviation of Yahweh = God, and probably gob = to protect, hence "God has protected".

Surnames derived from the name Giacomo

Some of these surnames are easy to recognize, but others are not. Many variants have lost their initial syllables on the left, or have had different suffixes added on the right:

• In the surname Pucciarelli, for example, only a "p" survives of the original root Jacopo.
• In Muccinelli or Muzzarelli, only the "m" of Giacomo has been preserved.

Surnames derived from Jacopo and from Giacomo are, according to A. Bongioanni and in order of increasing frequency: Bucci, Belli, Pucci, Pini, Betti, Bini, Di Giacomo, Baca, Bossi, Giacomelli, Bettini, Bello, Giacomini, Giacometti, Puccio, Giacobbe, Comilo, Petti. It should be noted that some of these surnames could also descend from Filippo or from other names, and that the surnames Bello and Belli could derive from the adjective.

These two names have given rise to countless surnames, among them Giacomo, Giacomi, Giacobo, Giacopo, Giacoppo, Giacobbi, Iacomo, Iacomi, Iacobo, Iacopo, Iapico, Iacovo, Iavoco, Iacobbi, Iacobbe. And, with the addition of prefixes: Di Giacomo, Dello Iacovo.

With the addition of suffixes there arose Giacomello, Giacomelli, Giacometti, Giacomino, Giacomini, Giacomin, Giacobini, Giacomìn, Giacomucci, Giacomuzzi, Giacomozzi, Giacomoni, Giacomazzo, Giacomazzi, Giacobelli, as well as Giacobini, Giocoboni, Giacobone, Giacobazzi, Giacopelli, Giacopetti, Giacopini, Giacopino, Giacopazzi, Giacovelli, Giacovazzo, Giacovani, Giappichelli, Giappichini.

Contracted forms

• In some regions, the name Giacomo was contracted into Giaco, and from there arose another set of surnames.
• In other regions, the contraction of Giacomo took its own particular form: Iaco.
• Through aphaeresis (the loss of an initial syllable), Giacomo becomes Como, with all its suffixed variants.

Dialect forms

• The dialect version of Giacomo gave rise to several suffixed surnames in northern Italy: Zacco, Zacchi, Zacchin, Zacchini, Zacchino, Zacchelli, Zacchetti, Zacchetto, Zaccola, Zacconi, Zacone.
• Other surnames could derive from the contraction of the hypocoristic Muzzo of Giacomuzzo.