This PhD thesis highlights the particular importance and vast potential of the right to good administration in the EU legal order and more particularly the capacity of this right of ensuring the procedural protection of individuals in the context of "composite" administrative proceedings. It also constitutes a contribution to the (polemic) debate on the difficult coexistence of the various sources of fundamental rights in the EU legal order. It highlights in this regard that there are instances where, even in relation to what might appear to be the same right, there are overlaps and sometimes clear differences as regards its content and level of protection according to its interpretation as a General Principle of EU Law (GPL) or as a fundamental right codified in the Charter of Fundamental Rights of the European Union (CFR). This thesis undertakes an in-depth comparative assessment of the protection of good administration as a Charter's right and as a GPL.