Thirty years ago, Anthony Downs spelled out a spatial theory of party competition that was already familiar, especially in continental European politics, dating back to the invention of the concepts "Left" and "Right" during the French Revolution. Despite the availability of the Left/Right scale as an empirical instrument, relevant research has failed to become cumulative, taking three divergent directions: one concentrating on ideology, another on self-placement data, and yet another on abstract mathematical models. When these isolated approaches are eventually integrated, it may indeed be shown that spatial theory is "a complete scientific theory," as was recently claimed. The Left/Right spatial framework holds such a promise even though some of the objections it has raised represent a true challenge for future research.