The world is not perfect—operational conditions, atmospheric properties, and component specifications are never truly deterministic and inevitably vary within certain ranges. Aircraft design optimization under uncertainties focuses on developing configurations that remain efficient, feasible, and constraint-compliant despite these variations. Modern approaches integrate robust, reliability-based, and possibilistic design optimization (RDO, RBDO, PBDO) methods, alongside surrogate modeling, to systematically address uncertainties in aerodynamics, weight and balance, and stability and control. This seminar will introduce these algorithms and demonstrate their application across various aircraft design problems, highlighting how uncertainty-aware design leads to more resilient and consistently performing aircraft.