While gender-based achievement gaps have been widely explored in academic motivation research, gender-related variables such as sexual orientation and other-gender similarity radically shift understandings of these disparities. Recent research has shown that gay men have a notable bachelor's degree attainment advantage over heterosexual men while bisexual women have lower attainment than heterosexual women. These differences have been shown to be partially related to gender atypicality, in particular, felt similarity to other genders (e.g., similarity to men among women, similarity to women among men). Despite these disparities and nascent other-gender similarity research, a lack of research has been conducted on academic motivation among sexual minority college students using educational psychology frameworks to better understand these differences. Thus, the current study utilized situated expectancy-value theory to explore: (1) differences in academic self-concept by gender and sexual orientation, (2) if other-gender similarity is related to academic self-concept and if this relationship differs by gender and sexual orientation, (3) if the relationship between other-gender similarity and academic self-concept is moderated by sexual orientation within gender groups, and (4) if general academic self-concept is associated with expectancies of success, subjective task value, and perceived cost in terms of completing one's major. Multiple group path analysis with a sample of 765 undergraduate students found a positive association between other-gender similarity and academic self-concept for heterosexual students only, but no other gender or sexual orientation-related differences in academic self-concept, as well as expected relationships between general academic self-concept, expectations of success, subjective task values, and perceived costs. While these results contribute to the use of multidimensional gender identity as a potentially important factor in situated expectancy-value frameworks of academic motivation, the findings should be considered within context of potential measurement flaws in current measurements of gender atypicality. Future work should continue to utilize robust theory from educational psychology while integrating interdisciplinary perspectives to improve understanding of academic motivation among sexual minority and gender atypical undergraduate students. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]