Ex-Arsenal goalkeeper Manuel Almunia and defender Fitz Hall have both signed one-year contracts, while five season-long loans - utilising the network of the club's owned by the Pozzo family - have also been agreed.
Midfielder Almen Abdi, along with forwards Matej Vydra and Steve Leo Beleck, have joined from Italian Serie A side Udinese, while Granada pair Daniel Pudil, a defender, and forward Ikechi Anya have arrived from Spain.
Hornets Technical Director Gian Luca Nani told the club's official website: "We expect these players to make a very positive impact on Gianfranco Zola's squad.
"We are constantly looking to add quality here at Watford and this is a task which will be ongoing throughout the season."
- Manuel Almunia
- Steve Leo Beleck
- Fitz Hall
- Daniel Pudil