The objectives of the thesis -which comprises six parts -can be summarized in i) implementing linear and nonlinear/nonparametric approaches toward detecting, measuring and analyzing the nature and directionality of causal relationships in financial markets, ii) elaborating on modern topics in financial investment analysis, iii) probing into the role of commodity futures in constructing optimal portfolios as well as iv) investigating growth dynamics via aggregated and disaggregated indices.The first paper named "Analyzing causal interactions between sectoral equity returns and commodity futures returns in the aftermath of the global financial crisis: The case of the US and EU equity returns", aims to explore and compare the dependence and co-movement structure between commodity and various asset classes' returns including the USA and EU stock markets via the use of linear and nonlinear causality testing in a comparative context with the additional adjustment for cointegration and conditional heteroscedasticity. The findings provide important implications for optimal asset allocation and portfolio diversification with respect to various market conditions, namely both in "good" and "bad" (crisis) times.The second paper is entitled "On the time scale behaviour of Equity-Commodity links: Implications for Portfolio Management", and has been published in the Journal of International Financial Markets, Institutions and Money (2016). The study is co-authored with Professors S. Bekiros, D.K. Nguyen, and B. Sjö. It develops a holistic framework for the investigation of the multi-horizon and intra-frequency causal directionalities of various asset classes, by means of multi-resolution analysis. The results verify the assumption that financial markets exhibit time-varying co-movement patterns, which are fundamentally important in a) generating profitable trading strategies according to different investor horizon expectations and b) decoding the financialization mechanism across various asset classes.The third paper entitled "Business Cycle (de) Synchronization in the aftermath of the Global Financial Crisis: Implications for the Euro Area", was published at Studies in Nonlinear Dynamics and Econometrics (2015) and is co-authored with S. Bekiros, D.K Nguyen and B. Sjö. In this work, the scaledependent time-varying (de)synchronization effects between the Eurozone and the broad Euro area business cycles are revealed, before and after the global financial crisis. The results, which point towards an increased observed co-movement during the crisis period for the Euro area, could be catalytic for the introduction of a more efficient monetary policy by EU institutions and in particular by the European Central Bank.In the fourth paper, "Do financial stress and policy uncertainty have an impact on the energy and metals markets? A quantile regression approach", which was published in the International Review of Economics and Finance (2016) and co-authored with J.C. Reboredo, the financial and policy uncertainty is investig...