2623 20160701171708.0 ASTROimport-780 Arias, M. L. 2007 Circumstellar Rings, Flat and Flaring Disks Emission lines formed in the circumstellar envelopes of several type of stars can be modeled using first principles of line formation. We present simple ways of calculating line emission profiles formed in circumstellar envelopes having different geometrical configurations. The fit of the observed line profiles with the calculated ones may give first order estimates of the physical parameters characterizing the line formation regions: opacity, size, particle density distribution, velocity fields, excitation temperature. Zorec, J. Frémat, Y. Active OB-Stars: Laboratories for Stellare and Circumstellar Physics 361 2007 419 http://esoads.eso.org/abs/2007ASPC..361..419A published in NONREF