This dissertation investigates the impact of central banks' asset purchase programs on the economy and the role of frictions in the corporate loan markets. It builds a series of models with trading and information frictions in goods market and credit market. Chapter 1 introduces the main idea in this thesis and presents a review on central banks' asset purchase programs and unconventional monetary policies. Chapter 2 constructs a model of the monetary economy with multiple nominal assets. Assets differ in terms of the liquidity services they provide. I show that the central bank can control the overall liquidity and welfare of the economy by changing the relative supply of assets. A liquidity trap exists away from the Friedman rule that has a positive real interest rate; the central bank's asset purchase/sale programs may be ineffective in instances of low enough inflation rates. My model also enables me to study the welfare effects of a restriction on trading with government bonds. Chapter 3 investigates the effects of open-market operations on the distributions of assets and prices. It offers a theoretical framework to incorporate multiple asset holdings in a tractable heterogeneous-agent model. This model features competitive search, which produces distributions of money and bond holdings as well as price dispersion among submarkets. At a high enough bond supply, the equilibrium shows segmentation in the asset market; only households with good income shocks participate in the bond market. Segmentation in the asset market is generated endogenously without assuming any rigidities or frictions in the asset market. Numerical exercises show that when the asset market is segmented, the central bank can improve welfare by purchasing bonds and supplying money. Chapter 4 develops a model of loan markets in which lenders post an array of heterogeneous contracts, then borrowers tradeoff terms of loan contracts and matching probability between themselves. I show that a unique separating equilibrium exists where each type of borrower applies to a certain type of contract. Chapter 4 also provides empirical evidence of both price dispersion and credit rationing in the corporate loan market. Chapter 5 offers concluding remarks and possible extensions. / Thesis (Ph.D, Economics) -- Queen's University, 2014-02-03 10:31:40.883