This thesis analyses different approaches to address the unemployment volatility puzzle. In the first two chapters, we develop two types of search frictions model with efficiency wages. The models can match observed fluctuations in unemployment and job vacancies in the U.S economy. Moreover, the models also capture labour market dynamics well. In the third chapter, we analyse two proposed solutions to the unemployment volatility puzzle: sticky wages and a small `hiring surplus'. We investigate a widely used calibration strategy in the literature and argue that it is a key factor in generating large unemployment volatility. In the fourth chapter, we reassess the following arguments on the unemployment volatility puzzle: strategic wage bargaining; large fluctuations in discount rates in the financial market; and endogenous job separations caused by idiosyncratic productivity shocks.