How important is a letter from your faculty adviser?

[Averroes MD]

Do PhD programs expect that one of your letters is from you faculty adviser? I've not used mine much and instead relied on someone else. I wanted to officially switch to this person but could not since this person was from another department/school within the university. 

 

Will not having a letter from my official supervisor be a red flag?

[drivingthoughts]

Well, at least in my case, for my ThM and PhD admissions, the directors told me that it was my faculty advisor's lengthy, detailed letter of recommendation that helped to float me into the pool for consideration. 

That said, if you don't have a strong relationship with your advisor, having them write you a short or impersonal letter would be bad. So, in my opinion, not having it would be a small red flag, but having a poor recommend would be worse.

[theophany]

Adcoms generally understand that master's students are assigned advisors that they may not have chosen, and that those relationships may be not so close. As @drivingthoughts said, you want strong letters more than anything else. By strong, that means thorough strong recommendations ideally from people well-known in the field (though this latter bit isn't always possible). If that's not your advisor, eh, not the end of the world. (And you have your statement of purpose to explain who you have actually studied with.) But if your advisor is well-known and in your field, it's a missed opportunity. It is letters and writing sample that make or break applications—the rest is mostly checking off boxes.

Edited February 23, 2016 by theophany

[Averroes MD]

Thanks for the input, both of you!