本研究探討董監事暨重要職員責任保險(簡稱：董監責任險)與資訊不對稱之間的關係。過去文獻關於購買董監責任險所獲得的利益以及所需付出的代價有許多的辯論。其中一種觀點認為購買董監責任險可以提供公司治理的監督機制以降低資訊不對稱程度，因此對股東有利。但是另一種觀點認為購買董監責任險會以減少董監事面臨訴訟時自己必須負擔的損失，因而可能會出現管理者機會主義行為而導致更多的道德風險問題。本研究採用股票市場中的優勢資訊交易機率(probability of information-based trading，簡稱PIN)當成企業資訊不對稱程度的直接衡量，以了解購買監責任險與資訊不對稱之間的關係。以2008年至2013年台灣上市公司為樣本之實證結果發現，整體而言，有購買董監責任險的公司，有較低的PIN值(也就是資訊不對稱程度較低)，基本上支持購買董監責任險確實可以提供公司治理的監督機制。然而在進一步比較有購買董監責任險公司以及沒有購買董監責任險的公司之後，結果顯示可能不太需要購買董監責任險的公司(以迴歸模型估計購買機率較低者)但實際上卻有購買時，相較於需要購買且實際上也有購買董監責任險的公司，會有相對比較高的PIN值(較高的資訊不對稱)。此結果顯示股票市場的PIN值確實會反應企業的投機行為，因此支持購買董監責任險依然會有出現道德風險問題的可能。本研究提供的證據顯示整體而言購買董監責任險具有公司治理的監督機制功能，但是道德風險問題還是可能會出現在某些購買董監責任險的企業。

此論文包含三大部分。第一部分探討董監事暨重要職員責任保險(D&O保險)的需求因素與公司治理等企業特徵間的關係，配合2003-2007年台灣上市上櫃公司的資料，研究影響公司是否購買D&O保險、保險限額與保險費的決策因素。實證結果證明，大型公司較需要D&O保險保障，且公司的董監事與利害關係人間存在代理成本問題。本文亦發現董監事獨立性等公司治理因素，對D&O保險購買行為有顯著影響，再則，公司的成長性及經理人風險趨避態度，都會影響保險限額的決定。本文結論進一步顯示訴訟風險對保險限額的決定有正向顯著的影響，而財務風險對D&O保險需求亦有若干影響力。第二及第三部分則進一步探討董監事暨重要職員責任保險對公司的行為或策略是否有影響。實證結果顯示D&O保險確實會影響公司風險承擔策略及公司財報方法的穩健性。 / This thesis is comprised of three essays on directors’ and officers’ (D&O) liability insurance, one interesting but little explored research area. Based on an unbalanced panel data set of public Taiwanese corporations in years 2003-2007, the first essay investigates the relationship between directors’ and officers’ (D&O) insurance demand and firm characteristics, especially corporate governance. The results suggest that large firms are more likely to purchase D&O insurance, and that there exists agency cost between directors/officers and stakeholders. The findings indicate that corporate governance, such as board independence, has an important impact on D&O insurance demand. Besides, the results show that growth opportunity or managerial risk aversion can affect the D&O insurance coverage amount. The litigation risk also has a positive and significant impact on the D&O insurance amount, and bankruptcy risk weakly influences the D&O insurance demand. In the second essay, I provide evidence regarding corporate business strategy by investigating the relation between directors’ and officers’ (D&O) insurance and risk taking behavior. This essay tries to test (a) whether firms are more active to adopt risk-taking strategies when their directors and top managers are covered by D&O insurance coverage; (b) whether the quality of corporate governance has influence on firm’s risk-taking behavior; and (c) whether insurers can distinguish D&O insurance purchases decision driven by managerial risk-taking behavior and charge adequate premium rate for such behavior. The empirical evidence suggests that D&O insurance coverage has a positive impact on firm risk-taking behavior. In addition, the results indicate that board composition may remarkably influence corporate risk-taking behavior. The preliminary findings also show that insurers can assess the induced risk-taking behavior ex ante and charge adequate premiums rate accordingly. In the third essay, I investigate whether the legal liability coverage result in the propensity of less conservatism and aggressive managerial behavior/strategy. More specifically, this study tests managerial opportunism behavior by examining whether the purchase of D&O insurance coverage is associated with more aggressive financial reporting strategy (i.e., less accounting conservatism). The empirical evidence suggests that D&O liability insurance purchase decision is positively associated with accounting conservatism. That is, firms with insurance coverage tend to recognize bad news in a timely manner, i.e. more earning conservatism. However, there is no significant relation between accounting conservatism and D&O insurance amount. In addition, the evidence shows that firms with strong board structure recognize good news faster than those with weak governance structure.