Abstract
This paper presents a brief review of photometric observations from 1565 A to 22 microns of Orion population stars. The data indicate irregular light variability and color excesses in all wavelengths. It is discussed some similarities and differences between Herbig Ae/Be stars and classical Be stars. It is concluded that the infrared excesses of T Tauri stars and related objects rise from different sources, such as, thermal radiation from circumstellar dust, bound-bound, free-bound and free-free emission processes originating in a hot ionized gaseous envelope surrounding the stars, infrared companions, and to a lesser extent interstellar extinction.
