The People’s Democratic Party (PDP) was established in 1998 at the time when Nigeria was under pressure from the international community to undertake political reform in preparation for anticipated return to civil rule. The PDP formed the first government after the country re-introduced civil rule in May 1999 and remained the ruling party at the national level and also in government in the majority of states of the federation until May 2015 when it lost to the All Progressives Congress (APC) in the presidential election, and unexpectedly recorded defeat in the other elections. The climax was on March 28, 2015 when Nigeria held its fifth presidential election and an incumbent president, Dr. Goodluck Jonathan was defeated by retired Major-General Mohammed Buhari who was contesting the presidential election for the fourth time. Apart from its remarkable victory in the previous four successive presidential elections, the PDP had a comfortable majority in the national legislature between 1999 and 2015. However, towards the end of President Obasanjo’s tenure, the party had started to experience disturbing cracks in its internal cohesion. It eventual defeat by the APC at both the presidential and state levels puts an abrupt end to the hegemony of the self-styled “largest political party in Africa” with a vision of “ruling Nigeria for sixty years”. This chapter presents analysis of the remote and immediate causes of the poor performance of the PDP in the 2015 elections. What are the remote and immediate causes of the defeat of the PDP in the 2015 elections? What was the nature of public support for the party and its presidential candidate? Was the dwindling public support for the party linked to its diagnostic analysis of the challenges of governance and development in the country? What was the role of the Jonathan presidency in the political misfortune of the party? What was the capacity of the party to cope with some of the changes and innovations in the electoral process that may have contributed to the outcomes of the 2015 elections? How has the PDP faired since the inauguration of the new APC-led government? Is the party adjusting well to playing the role of an opposition party? How well has the party faired in this regard, and what are the lessons learned? And finally, how does the electoral misfortune of the PDP helps us to understand the strength and weaknesses of the democratic institutions in Nigeria? As many are these questions that one consider useful for understanding the party system in modern Nigeria.