The literature highlights how different individual levels of political interest and knowledge matter for political attitudes and behavior. A logical-quantitative voting model is thus proposed for a two-party system, based on voters' left–right ideological positions and their degree of political involvement. The model hypothesizes that although more involved voters generally behave in accordance with their ideological orientation, those who are less involved do not. Moreover, the latter tend to be more undecided and therefore likely to be more strongly influenced by campaign activities. This model is then applied to survey data regarding the 2001 Italian general elections. Results confirm the hypotheses and show that the most competitive area is ideologically a narrow centrist area for very involved citizens, becoming wider as the level of involvement decreases. Separate analyses are carried out for different geopolitical areas of the country, with results fitting the political history of these areas.