How do Italian object pronouns work?
Direct object pronouns — lo, la, li, le — replace the thing acted on. Indirect ones — gli, le, and gli again in the plural — replace the person receiving it. They go before the conjugated verb or attach to an infinitive. When both appear, the indirect comes first and changes form: mi lo becomes me lo, and gli lo becomes glielo.
Direct against indirect
The direct object is what the verb happens to; the indirect object is who receives it. Italian marks the difference in the pronoun, and the third person is where it matters most.
Vedo il libro. → Lo vedo.
I see the book. → I see it.
Do il libro a Marco. → Gli do il libro.
I give Marco the book. → I give him the book.
Do il libro a Maria. → Le do il libro.
→ I give her the book.
Where they go
Before the conjugated verb, always. With an infinitive they attach to the end and the final -e drops. With affirmative informal commands they also attach.
Lo voglio vedere. / Voglio vederlo.
I want to see it.
Both correct.
Dimmi!
Tell me!
Attached to the command.
L'ho visto.
I saw it.
Before the auxiliary, elided.
Combining them
When both pronouns appear, the indirect comes first and its final vowel changes to e. The third person forms fuse into a single word: glielo, gliela, glieli, gliele — used for both him and her.
Me lo dai?
Will you give it to me?
mi + lo = me lo.
Te la mando.
I'll send it to you.
Glielo dico.
I'll tell him/her.
One word, and the same for both genders.
Common mistakes
Gli lo dico.
Glielo dico.
The third-person indirect fuses with the direct pronoun into a single word.
Mi lo dai?
Me lo dai?
Before another pronoun, mi becomes me. The same applies to ti, ci and vi.
Voglio lo vedere.
Voglio vederlo. / Lo voglio vedere.
The pronoun attaches to the infinitive or precedes the conjugated verb, never sits loose between them.
Frequently asked questions
Does the participle agree with the object pronoun?
With third-person direct pronouns, yes: l'ho vista for a feminine object, li ho visti for masculine plural. With mi, ti, ci and vi agreement is optional and both are heard.
Why is glielo the same for him and her?
The masculine and feminine indirect forms both collapse into glie- when they combine with a direct pronoun. Context does the disambiguating, and Italians rarely find it ambiguous.
How does this compare to Spanish?
Structurally very similar — both put pronouns before the verb, both fuse the pair, both attach to infinitives. Spanish uses se where Italian uses glie-, so the mechanism matches even though the forms do not.