What is the difference between stage monitors and in-ear monitors?

Stage monitors (wedges) are speakers placed on the stage floor angled up toward the performers. They project the monitor mix into the stage area so performers can hear themselves. Wedges are simple, reliable, and familiar, but they add volume and potential feedback to the stage environment.

In-ear monitors (IEMs) are personal earpieces connected to a wireless bodypack receiver. Each performer gets a custom mix delivered directly into their ears. IEMs offer dramatically better isolation, reduce stage volume, eliminate monitor-related feedback, and allow performers to hear detail that wedges can't deliver in a loud stage environment. The tradeoff is higher cost, more RF channels to coordinate, and the need for well-built individual mixes to avoid the "isolated in a bubble" feeling some performers dislike. For concert touring and large-scale productions, IEMs are the standard.