and cultural barriers to enrollment and persistence among under-represented groups remain obscure or unaddressed, such programs cannot succeed" (Seymour 13 , p. 8). And there is an ethical dimension to the choice to focus on recruitment: while controversial, many studies show that the university SME environment is unfriendly, even hostile, to women engineers. Thus, is it ethical to recruit women into a field of study that they are likely to find discriminatory? Yet, representation will continue to be a problem if no recruitment efforts are performed. A resolution can be found in the manner of "recruitment" employed. If "recruitment" is done with a "push-in" approach-marketing SME to women and girls despite its differentially inhospitable environment-then those women may unduly suffer and the "pipeline" will develop "leaks." But if "recruitment" is thought of as a "pull-in"-changing the undergraduate SME environment so that it treats women fairly and is even attractive to them-then representation is increased without undue risk of suffering and "leaks." An engineering analogy applies: to increase the flow in a pipe, one could 1) apply more pressure to the supply side of the pipe or 2) increase the diameter of the pipe. The former results in excess stress on the medium, strain on the pipe, and leaks. The latter just results in more flow, though it does require a new pipe. The required changes to increase the women-friendliness of SME are considerably more complex than increasing the diameter of a pipe. Thus, the first step in improving representation is to understand the dimensions of women's experiences in the SME culture: social, cultural, academic, interpersonal, and intrapersonal. There are a multitude of factors, forces, and structures associated with women's underrepresentation in undergraduate SME-more than can be covered in one literature review. This review examines three factors which are among the best understood and considered most important: ability, self-efficacy, and discrimination. To put these in context, a full literature review would also include these topics: expectations, enjoyment, contextualized knowledge, congruence, role-conflict, competition, group work, and support. The focus of this review is on the undergraduate years, though it provides a brief overview of pre-college factors to inform the undergraduate experience. This focus is not to downplay the importance of the pre-college, graduate school, faculty, or industry research literatures on WIE; these must be understood for an overall assessment of women's experiences in engineering. This review aims to stay as close to the actual research data as possible. Author's interpretations are given less weight than actual results. Whether null hypotheses are rejected or not rejected, those results are reported and incorporated with the other results for a particular topic. When factors are found to be significant, an attempt is made to quantify that factor in some way, either by the level of the difference or its correlation to another factor....