二〇〇五年十一月，德意志聯邦共和國出現歷史上第二次大聯合政府，即使梅克爾大聯合政府中，兩大黨於聯邦議會的席次率將近73%，但仍出現聯盟黨與社民黨衝突不斷，社民黨之黨員數、政黨支持度大幅滑落，與兩大黨邦議會選舉結果大多不佳的狀況。另外，聯邦層面在野的自民黨、左黨、綠黨則各自保持約10% 的實力，並蓬勃發展。五黨的政黨體系已經在聯邦與邦層面中生根，跨左右政黨分歧的聯合政府型態在邦政治中也不是新鮮事。針對前述大聯合政府不同於一般最小獲勝聯合政府的穩定情勢，本文先探究梅克爾大聯合政府的立法決策模式；並藉由｢否決者理論｣，依據否決者數量，否決者意識型態或立場的差距，與內部的融合度，來探討此一大聯合政府決策體系中的黨政關係、政策改變情形，和該時期政治體系的穩定度，以及該大聯合政府對德國政治之影響。

Grand coalition parties—the Union Party (CDI+CSU) and SPD— currently hold approximately 73% of the seats in the German Bundestag, but are nonethelress beset by many conflicts and problems, including decreasing party membership, falling popular support and poor election results in local parliaments. Moreover, the three oppo-sition parties—FDP, die Linke and the German Green party—can currently claim around 10% support in polls. In effect, since No-vember 2005, there has been a five-party system in place not only at the federal level, but also contesting local government elections. Meanwhile, a CDU-Grünen coalition has emerged at the local level in Hamburg. These strange conditions make Merkel’s grand coalition different from the minimum winning coalitions typically seen in stable political systems. This research considers the impact of Merkel’s grand coalition on German politics, examining the political proce-dures and applying “veto player theory”: number of veto players, distance of different ideologies, and intra-cohesion grade of veto plays. This provides insight into how Merkel’s grand coalition oper-ates, why its policies have changed and why there has been a decline in political stability.