PIGEON is interface software that links Python and MATLAB optimizers to environmental simulation models. With execution of Pigeon, a number of Python optimizers can be seamlessly utilized, including optimizers from the scipy optimization libray as well as numerous other freely available codes. Similarly, numerous MATLAB optimization toolboxes can be used, including those available in the standard Optimization Toolbox, the Genetic and Evolutionary Algorithms toolbox (GEATbx), the Global Optimization Toolbox, and the Direct Search Toolbox.