In this work we report on the in situ investigation of MBE grown ZnSe surfaces performed simultaneously by reflectance anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED). Reconstructions and anisotropic reflectance of the ZnSe(001) surface are studied in the temperature range from 50 degrees C to 380 degrees C. With increasing temperature the ZnSe surface evolves from a Se-rich c(2x2)(Se) via a Se-rich (2x1) to a Zn-rich c(2x2)(Zn) surface reconstruction with the transition temperatures depending on whether the surface is Se stabilized or not. Each surface reconstruction as verified by RHEED is accompanied by a characteristic RAS spectrum. Time resolved measurements of the RAS signal at fixed photon energies allowed to determine the activation energy (0.7 eV) for the Se desorption from the (2x1) reconstructed ZnSe(001) surface.