The thermonuclear supernovae are unique among all other supernovae because they derive their explosion energies from nuclear energy release instead of the gravitational collapse of massive stellar cores. Core-collapse supernovae, the explosive final moments of massive stars, are complex, dynamic, multiphysics problems coupling all fundamental forces to produce a bright explosion from the birth of a neutron star or black hole. Simulating thermonuclear supernovae is complicated by a range of length scales that spans more than 10 orders of magnitude. FLASH was developed initially under the aegis of the Department of Energy /Advanced Simulation and Computing Academic Strategic Alliance Program, under the Advanced Scientific Computing Initiative at the Center from Astrophysical Thermonuclear Flashes at the University of Chicago. FLASH is written primarily in Fortran, with some C and a Python script for building applications and utilizes the Message Passing Interface library for distributed-memory parallelism.