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The HII region of M17 interacts with a huge adjacent molecular cloud. During a deep JHKL survey with the VLT, about 650 extremely red objects (1.5 < K-L < 6.8) have been discovered which are interpreted as accreting protostars. The objects suffer from heavy extinction; however, a large fraction of their red colour originates from hot circumstellar dust. In comparison with other young clusters (e.g. Trapezium, NGC 2024), the protostellar population in M17 is the largest and "reddest" one detected so far. The sample comprises sources with X-ray emission and covers the entire mass range. Among the high-mass objects there is a hyper-compact HII region (B0), an O6 star with a circumstellar disk and an H2O maser source.
The protostellar objects occur predominantly along the northern and southwestern interface of the HII region with an associated molecular cloud. We discuss this population of accreting protostars at the periphery of the cluster in the context of ongoing star formation triggered by the central O stars in M17.
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