The author discusses in detail the role of the two-party model in the political system of the USA. The American two-party system always flexibly responded to radical challenges of the times, neutralizing radicalism by means of liberal manoeuvre. Two principles, consensus and alternativeness, underlie the relationships of the two bourgeois parties, Democratic and Republican. Mutual consent in evaluation of the foundations of the American social and political systems and political culture, secures evolutionary development of the socium and continuity in the functioning of its institutions. Alternativity of the methods the parties suggest for the improvement of society, for economic growth, for the achievement of social compromises and stability, creates real competition in the political market, it enables Americans to choose the better political “ware”, weakens or neutralizes the competitiveness of small political “sellers”. And yet, the author stresses, the American two-party system isn’t adequate today to be able to reflect the whole range of social ideas and positions. Since the middle of the 20th century there has taken place drastic growth of the activity of interest groups which, to a certain extent, fulfill the functions of third parties once ousted from the historical scene.