Four extraterrestrials, X-1, X-2, X-3 and X-4, arrive on Earth in the early sixties. Here they decide to take on human features to study the terrestrials incognito, but end up getting involved in the Roman "dolce vita".
| Directing | Pipolo | Director |
| Directing | Castellano | Director |
| Production | Dario Sabatello | Producer |
| Camera | Alfio Contini | Director of Photography |
| Editing | Gisa Radicchi Levi | Editor |
| Art | Ramiro Gómez | Production Design |
| Art | Massimo Tavazzi | Set Decoration |
| Costume & Make-Up | Cesare Rovatti | Costume Design |
| Costume & Make-Up | Amato Garbini | Makeup Artist |
| Costume & Make-Up | Rosa Luciani | Hairstylist |
| Production | Sergio Iacobis | Production Manager |
| Directing | Emilio P. Miraglia | First Assistant Director |
| Directing | Marcello Pandolfi | Second Assistant Director |
| Camera | Maurizio Scanzani | Camera Operator |
| Editing | Marina Sacco | Assistant Editor |
| Production | Renato Rizzuto | Production Secretary |
| Writing | Castellano | Story |
| Writing | Castellano | Screenplay |
| Writing | Pipolo | Story |
| Writing | Pipolo | Screenplay |
| Sound | Ennio Morricone | Original Music Composer |
| Editing | Petra de Nieva | Co-Editor |
| Art | Giorgio Giovannini | Production Design |
| Production | Manuel Pérez | Line Producer |
| Production | Carlo Bartolini | Unit Manager |
| Directing | Sinesio Isla | Second Assistant Director |
| Sound | Luigi Puri | Sound |