Law No. 270 of 21 December 2005 introduced a fully proportional system for election to the Chamber of Deputies, with the possibility of the award of bonus seats for a nationwide majority result, replacing the earlier partly proportional system.
The 617 Deputies are elected nationwide in proportion to the number of votes obtained by the lists of candidates submitted in the 26 constituencies; one Deputy is elected using the first-past-the-post system in the single-member Valle d'Aosta constituency; the remaining 12 Deputies are elected to the Constituency for Italians living abroad following the procedures provided by Law No. 459 of 2001 and its regulation for implementation (D.P.R. Decree of the President of the Republic - No. 104 of 2003).
The new rules provide that with regard to the candidates, the political parties submitting lists may also form coalitions; parties intending to stand for election to the position of ruling party must also submit their manifesto and announce the name of their leader.
The voting procedure permits voters to cast only one vote on their preferred list, with no preference votes.
The seats are distributed proportionately nationwide between the coalitions of lists and the lists that have exceeded the statutory minimum thresholds. Only coalitions obtaining at least 10% of the total valid votes cast shall be admitted to the distribution of seats, and within these coalitions, the lists obtaining 2% of the valid votes cast, the linguistic minorities' list obtaining at least 20% of the votes cast in their constituency and the list obtaining the highest number of votes among all the lists which fail to win 2% of the votes cast. Lists which are not attached to a coalition are also admitted for distribution of seats if they obtain at least 4% of the votes nationwide.
In the event that the coalition of lists (or the non-attached list) with the largest number of votes fail to win 340 seats, they are awarded a number of "topping-up" bonus seats to reach 340.
The seats are distributed in the following phases: