The present dissertation analyzes fundamental theoretical controversies related to the concept and the justification of corporate taxation. It focuses on legal, historical and public finance aspects of two legal systems: a continental one (Swiss law) and an Anglo-Saxon one (US Law). Part I focuses the analysis of the entity classification rules for corporate tax purposes: which entities are subjected to the corporate tax and under what rules. We conclude that no absolute common feature exists that would justify why certain entities are corporate taxpayers whereas others are not. Part II analyzes legal, philosophical and economic justification and criticisms of the corporate tax: why certain entities are subjected to corporate taxation. We identify several fundamental theoretical and practical controversies of the corporate taxation, such as incompatibility with the principle of individual ability to pay and distortion of the effects of the individual income taxation of corporate stakeholders (not only shareholders).