1. With the verb essere the past participle agrees with the subject, both in number and gender.
- Gloria è andata in discoteca sabato sera.
- Gloria went to the disco on Saturday night.
- Siamo tornati dalle vacanze da poco e ora non abbiamo voglia di lavorare.
- We have just returned from vacation and now we don’t feel like working.
- Maria è andata via.
- Mary has gone away.
2. When the past participle is preceded by the direct object the agreement is optional.
- Vi hanno sentito/i cantare giovedì sera a teatro.
- They heard you singing on Thursday evening at the theatre.
3. When the past participle is used as an adjective.
- Aveva i piedi infangati.
- His feet were muddy.
- Se ti arrabbi, avrai una vacanza rovinata.
- If you get angry, your vacation will be ruined.
4. With the verb avere, when there are the pronouns lo/la /li/le/l’ the agreement is obligatory.
- Le ho viste ieri sera in piazza.
- I saw them last night in the square.
- Mario l’ho visto ieri, ma Lia non l’ho vista.
- I saw Mario yesterday, but I didn’t see Lia.
- I ragazzi non li ho accompagnati, mentre le ragazze le ho fatte andare con la zia.
- I didn’t accompany the boys, while I made the girls go with their aunt.