The first chapter of my thesis explores monetary policy in a New Keynesian model with Markov-switching risk aversion. The second considers the implications for the macroeconomic and financial properties of an RBC model of the presence of habit formation. The third examines the result of adding the ``Tobin constraint" that shares equal the capital stock to a benchmark RBC mdoel. The underlying theme of these endeavors is rendering macroeconomic models more realistic via the introduction of time-varying preferences, non-linear modelling, and financial frictions.