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Although the massive stars are perhaps the most striking because of their brightness, they are relatively few in number, and the nearest regions in which they are forming are distant. The nearest region, the Orion Nebula, is 500 pc in distance, and even resolutions as high as one arc second yield linear resolutions of only 500 AU. At the same time, the high mass stars reach the Main Sequence while they are still heavlily imbedded in the clouds from which they form, and they must be studied at the long wavelengths which penetrate the clouds. These are infrared and radio wavelengths. The development of radio interferometers, such as the VLA operating at centimeter wavelengths, has profoundly changed our ability to study these processes in some detail. Our knowledge of the compact HII regions surrounding young O Associations is one example of the riches brought by this technical development. The discovery two decades ago that the dust clouds contain significant traces of polyatomic molecules led to the detection of the Giant Molecular Clouds and the realization that the detailed properties of the clouds and the star formation process could be understood from observations with interferometers at millimeter wavelengths.
