EN
Operational risk is defined as the possibility of incurring losses resulting from the failure, deficiency or inadequacy of internal processes, people and systems or from external events. In practice, the most important source of operational risk is when an authorised employee becomes a rogue trader, making unfair and usually unauthorised trades. The main purpose of this paper is to compile and analyse case studies of selected financial disasters caused by unauthorised transactions. The structure of the paper is thus built on the analysis of the individual cases: Daiwa, Sumitomo, Orange County, Allied Irish Bank, Amaranth Advisors, and Société Générale. Each case is presented following the same scheme: historical background, rogue trader strategy, conclusions. I summarise the most important causes of financial disaster and suggest guidelines for preventing similar situations in the future.