Poly(ethylene vinyl acetate) (EVA) is a very common polymer used in hot melt adhesives. The rheological and thermal-mechanical properties of these adhesives are strongly related to the content of vinyl acetate (VA) incorporated into this random copolymer during polymerization. Results of in-line monitoring of VA content in flowing molten EVA polymers, using fiberoptic near infrared spectroscopy, shall be discussed in detail. In-line monitoring is not only desired for its numerous advantages (such as high quality products, lower waste, lower developmental cycle time, and lower costs) but also because it eliminates the sample handling concerns associated with molten polymers.