This thesis consists of three essays on business cycle fluctuations that are based on the market-clearing dynamic general equilibrium framework. The first two essays examine the ultimate source of economic fluctuations in Thailand and Australia, respectively. The tool of study is the Business Cycle Accounting (BCA) method developed by Chari et al. (2002; 2007a). The third essay investigates the relation between capital-labour substitution and sectoral externalities in self-fulfilling expectation equilibria. It employs a two-sector competitive model proposed by Benhabib and Farmer (1996). The BCA method examines the transmission mechanisms of shocks within an economy. These transmission mechanisms are called wedges which are responsible for ...