This paper series aims at improving the general knowledge about what led to the recent global financial and economic crisis, how the crisis unfolded and what the EU has done and is currently doing to mitigate its consequences and to ensure that a similar situation will not happen again in the future.This first block, "The origins of the financial crisis", includes some basic economic concepts (such as the institutional sectors with their economic functions and interconnections or the economic cycle) and some basic concepts about the organisation of the EU (the legislative process, the institutional triangle and the principles of subsidiarity and proportionality). It then documents how imbalances and risks were build-up over the years. Finally, it explains how the crisis was triggered by the sub-prime segment in the US and how it spread to other jurisdictions and sectors, including the doom loop of subdued economic growth, weak financial sector and stressed public accounts.