Co-ownership is a system whereby two football clubs own the contract of a player jointly, although the player is only registered to play for one club. It is not a universal system, but is used in some countries, including Italy, Argentina, Chile and Uruguay.
This type of deal differs from third-party ownership, in that in the latter, the player's contract is owned by a non-footballing entity, such as a management company.
The use of co-ownership deals in Italian football has been described as "common". They are regulated by Article 102 bis of FIGC Internal Organizational Regulations (Norme Organizzative Interne della FIGC) and are officially known as rights of participation (diritti di partecipazione). For a co-ownership to be set, a player must have at least two years left in his current contract. The co-ownership deal itself will last one season — though it may be terminated early — after which the two clubs shall decide whether to renew or to terminate the deal. Should they fail to reach an agreement, the issue shall be resolved via a blind auction. In case none of the clubs submit a bid, the rights to the footballer shall remain to the club who had the actual use of the player during the season.
When a player is in co-ownership between two teams, he can still be sent on a free loan to a third side, provided that both the owning clubs agree on the move. Besides, the one of the two clubs not owning the actual use of the footballer is allowed to sell his half share to another club, still provided that the other owning club and the player agree.
An example of co-ownership in practice was when the Brazilian player Adriano was co-owned by Inter and Parma. Inter sold a half share in Adriano to Parma for £4M, who had the use of the player and had to pay his wages. If there had been a dispute over the rightful ownership of the player, it would have been settled by sealed bidding. Adriano had great success at Parma, which meant that Inter later paid £13.5M to buy out Parma's half share.