Making doctoral education accessible and successful for students from low income, first generation families as well as members of immigrant or specific ethnic groups is a world- wide problem. In the US the traditional explanation for the low numbers of Ph.D. recipients from these groups are lack of preparation, lack of interest and a "leaky pipeline." These alone are not enough to explain disparities. This article argues that the most powerful vehicles of exclusion are tacit knowledge and the implicit bias of faculty and is related to doctoral/faculty socialization. Faculty share the values and prejudices of the broader society and those of their own group--one which in the US is predominately white, male and from well-educated middle class families. Their identity as "faculty" of a particular discipline and as members of a profession legitimizes their capacity to evaluate and judge matters within their discipline and their professional responsibilities. Most faculty tend to believe they are objective and even "scientific" in their judgements. Nonetheless, in the course of their lifetimes they have acquired tacit knowledge within the range of their experiences that can be expressed as "implicit bias" and is now documented. The result may be variable responses to students based on their personal characteristics, not their academic merit. Since faculty are to a great extent similarly socialized into their profession in many countries, this model for understanding a major source of discrimination could be potentially useful beyond the US, even if doctoral training is formally organized differently elsewhere. Faculty everywhere are the gatekeepers.