Since the onset of the economic crisis, parties in parliament (especially those in opposition) have found themselves faced with a dilemma: choosing between the need to cooperate with the government in order to overcome the crisis and the opportunity provided by a weakened government to stress their adversarial position so as to be more easily reelected and possibly get into power. What have they decided to do? The present contribution introduces a collection of works exploring this dilemma in southern European countries, by examining the opposition behaviour in Greece, Italy, Portugal and Spain; and in the European Parliament.