BETSEE (BioElectric Tissue Simulation Engine Environment) is the open-source cross-platform graphical user interface (GUI) for BETSE, a finite volume simulator for 2D computational multiphysics problems in the life sciences – including electrodiffusion, electro-osmosis, galvanotaxis, voltage-gated ion channels, gene regulatory networks, and biochemical reaction networks (e.g., metabolism). Like BETSE, BETSEE is portably implemented in pure Python 3, continuously stress-tested with GitLab-CI × Appveyor + py.test, and permissively distributed under the BSD 2-clause license.