Hugo Campagnaro, Marco Andreolli and Juan Pablo Carrizo have joined the club from Napoli, Chievo and Lazio, respectively, having run down their contracts at their former clubs.
Carrizo's summer move to San Siro has been known about since March, when the 29-year-old goalkeeper signed a pre-contract agreement to leave Lazio.
Campagnaro, 33, chose to follow new Inter coach Walter Mazzarri - who replaced Andrea Stramaccioni as coach at the end of last season - from Napoli this summer.
Ex-Chievo defender Andreolli put pen to paper on a four-year deal with the Nerazzurri, though the 27-year-old had been set to join the Serie A side since February.
In addition to the trio of free agents, Inter has signed up young attacking prospect Alessandro Capello, who is expected to be placed in the Primavera squad.