This thesis examines the capital structure choice of Australian firms with an emphasis on the impact of market timing and liquidity considering 1438 available firms for the period, 1997 to 2005. The relationship between capital structure and its determinants is the main focus of this thesis, with four empirical analyses. These analyses are all conducted within the Baker and Wurgler (2002) and Hovakimian (2006) models with both pooled ordinary least squares (OLS) and fixed effect panel analysis. The theory of market timing introduced by Baker and Wurgler (2002) has received considerable attention in recent years. Baker and Wurgler (2002) contend that past market timing has a long lasting impact on capital structure and thus, capital structure is the cumulative outcome of the past attempts at equity market timing. This thesis examines the Baker and Wurgler (2002) argument in an Australian context. It is found that the variation in leverage was explained by the market-to-book ratio and the effect of market-to-book ratio was explained by equity issues as market timing theory implies. However, the results are sensitive to data sample choice with variation in the strength of the negative relationship observed between external finance weighted average market-to-book and leverage. This suggests that while market timing appears to affect capital structure choice, it does not support the hypothesis that past market timing decisions have a long lasting impact on Australian firm capital structure. Hovakimian ( 2006) questions the Baker and Wurgler (2002) conclusion about firm behaviour and finds evidence that past market-to-book ratio has a significant impact on current financing decisions because it contains information about growth opportunities, not captured by the current market-to-book ratio. This thesis also examines the Hovakimian (2006) argument and finds evidence to support the argument of Hovakimian (2006) that, growth opportunities provide a reasonable explanation for the past market-to-book ratio effect for Australian firms. Analysis also focuses on broad industry differences. And it is found that there are significant differences between mining and non-mining firm in the determinants of capital structure. Finally, the impact of liquidity on Australian capital structure choice is analysed within the context of the Baker and Wurgler (2002) and Hovakimian (2006) models. It is found that liquidity is important to a firm's leverage choice. There is evidence that liquid firms tend to have lower leverage. Further, while liquidity has little effect on the sensitivity of leverage to market-to-book for Baker and Wurgler (2002) filtered data, a liquidity effect is evident in a broader set of four standard deviation filtered data. It is also found that greater liquidity is associated with less sensitivity of leverage to cash flows and that the asset tangibility relation with leverage is also sensitive to liquidity. Finally, there is evidence that more liquid firms are more sensitive in their tendency to revert to some long run leverage value.