本論文主旨在於探討有關於大股東交易的兩則議題：下單策略與股票質押交易。在第一篇文章中投資者在證券市場可以使用市價單或限價單進行交易。有流動性需求的大股東急於成交，必須使用市價單。擁有優勢訊息的大股東則能自由選擇委託單之形式，如以市價單進行交易，則能利用流動交易者作為掩護，避免私有訊息反映至價格上。限價單雖無此掩護，但限價單可以藉由價格的波動找到有利的價格，以便逐價套利。本文發現當市場資訊不對稱嚴重（即當大股東擁有重大利多或利空消息）、資訊精確度較高與知訊人數較少時，大股東傾向使用市價單；若散戶的避險需求變異增加，致使價格波動較大，則大股東就會使用限價單。
第二篇文章則分析公司大股東與銀行間私人借貸契約中，利用斷頭條款的設計如何影響其在股票市場的交易行為，進而透過影響股價而改變公司的投資效率。當公司缺乏足夠內部資金而必須舉債融通新的投資計劃時，股價揭露的訊息有助於債權人評估公司債信，作為融通決策的參考。因此股價會影響公司的融資成本，進而影響公司的實質價值。擁有優勢情報的大股東因而有動機在投資計劃品質不佳時，進場護盤操縱價格，以誤導債權人對公司計劃品質的認知。而大股東與銀行之間斷頭條款的約定，或能促使銀行搜集訊息，並利用訊息做出斷頭的決定，或是藉由質押股票的賣出，減少大股東的持股，從而降低大股東操縱股價的誘因。因此斷頭條款的存在增進了股價資訊性，有助於債權人做出更正確的融資決策，提升公司的投資效率，進而使大股東的財富增加。

This dissertation contains two essays on the trading behavior of informed large shareholders. The first essay studies the information content of the order forms selected by a large shareholder whose trade may be motivated by either liquidity shocks or superior information. The large shareholder can submit either market or limit orders. A liquidity-based large shareholder must trade a certain quantity during a fixed period of time, and to fulfill this goal she must submit a market order. By submitting a market order, an informed large shareholder can pool with her liquidity-based counterpart, thereby reducing the cost of trading. On the other hand, a limit order (or a general demand schedule) may reveal the informed large shareholder''sidentity, but by allowing different quantities to be traded at different prices, the limit order may still yield a higher return for the informed large shareholder when the latter is faced with the hedging demand from risk averse small traders. We show that large informed shareholders tend to prefer market orders to limit orders, (1) when she receives extremely good or bad news; (2) when her signal is very precise; and (3) when most traders in the market are uninformed. On the other hand, limit orders are preferred when the hedging demand is volatile.
The second essay asks how a large shareholder''s personal loan relationship with a bank may affect her stock trading behavior and impact on the firm''s investment efficiency. With little internal fund the firm must raise money from a competitive financial market to finance a new investment project of which the quality is privately observed by a large shareholder. Before observing the project''s quality, the shareholder signs a debt contract with a bank, where the contract requires a number of shares as collateral and allows the bank to liquidate the collateral in the event that stock price falls below a pre-specified level. We show that the large shareholder''s personal borrowing from the bank can serve as a commitment which brings the bank into the stock market as an active informed trader whose decision regarding whether to liquidate the collateral enhances the information content of the equilibrium stock price. With the stock price becoming more informative, the agency problems between existing shareholders and the new claimants are mitigated, which in turn raises the firm''s investment efficiency and increases the large shareholder''s wealth.