Two hundred and fifty-five stars showing emission in Ha have been observed in an area of 3.5 square degrees which contains the brightest part of the Orion Nebula. The distribution and frequency of these emission stars seem to be correlated with the general shape and differing intensity of the bright nebulosities of this region. At the same time the existence of a dense stellar group provisionally called the "Orion Nebula Cluster' `-centered at the Trapezium stars is strikingly revealed. Fourteen peculiar objects, most of them stars imbedded in nebulous material, have been found in the same area. One of these is probably a new faint cometary nebula. The apparent coexistence and concentricity observed between the Nebuia and the densest group of emission stars suggests a tentative hypothesis of the formation of late-type dwarf stars from the Orion nebular material.