In watches, as in life, finding the right partner can be hard. For most elite watchmaking houses, the celebrity ambassador is as de rigueur as the balance wheel. Those ambassadors can serve a number of purposes—chief among them creating some hype–and no hype-machine is as complicated or potentially awful as the “collaboration watch.” The trap, of course, exists in the fact that celebrities are not watch designers, and in some cases a celebrity’s taste may not be in perfect alignment with the brand’s tenets, or their taste may just be, well, not that great. There have been a few clunkers along the way, to be sure.

Presumably, the collaboration watch actually brings the star in question into the design process—or so we are told. The extent of the star’s involvement is never fully detailed, and the occasional interview and/or testimony on the collaboration process typically serves as the only documentation of what was involved. Some, like John Mayer, are clearly watch-crazy and have obviously had a strong hand in the design, but others remain a bit more mysterious. Artists and architects are obvious bedfellows, but many singers, actors, and athletes have added their two cents to the world of haute horology. Here we’ve rounded up 10 of the most notable celebrity watch collaborations.