Today, more individuals are seeking to learn a second language (L2) or foreign language (FL) than ever before. These individuals are language learners who intend to use their growing L2 knowledge to traverse linguistic and national boundaries in order to achieve their personal and professional goals (Callahan & Gándara, 2014). To realize these goals in the digital era, L2 learners must be more prepared than ever to use their knowledge with written media, making L2 reading a central skill to successful use of their L2 knowledge. Yet, when language learners attempt to use their L2 skills in their daily lives, they are often unable to diagnose their own strengths and weaknesses, making the task of comprehending a complex text challenging. In order to develop learner autonomy where learners are capable of overcoming such challenges, the learners themselves must be involved in their own assessment (Little, 2009). Therefore, with these two intersecting skills of L2/FL self-assessment and reading, at present there is a need to expand examinations to investigate the variables that shape these constructs in concert across varied contexts of language learning. The following dissertation contributes to this understanding by (1) examining self-assessment through innovative methodological approaches and pedagogical interventions and (2) analyzing the intersecting and interacting variables that impact L2 reading comprehension in varied contexts of language learning with adolescents and adults. Specifically, these studies investigate the learners' abilities to accurately self-assess their L2 reading capabilities through three separate studies of L2 reading and self-assessment.Building from prior examinations of these constructs, this dissertation uses quantitative methodology to investigate the connections among topic familiarity, assessment methods, text formats, self-assessment, and L2 reading comprehension (Brantmeier, 2006b; Brantmeier et al., 2012; Brantmeier, Stube, & Yu, 2014; Lee, 1996; Pulido, 2007; Wolf, 1993). In order to examine test methods, L2 reading comprehension is measured through multiple response paradigms throughout the dissertation, providing a robust understanding of L2 self-assessment as it is associated with different assessments of L2 reading comprehension (Alderson, 2000). Traditional and advanced statistical procedures are employed to robustly answer the questions presented in these studies (Plonsky, 2015).Findings indicate that language learners (1) have variable capabilities in L2 reading comprehension, even when they are placed at the same level of instruction. Further, learners (2) may be able to accurately self-assess with and without training, particularly when afforded criterion-referenced self-assessment items and when such self-assessments are aligned with learners' prior test-taking experiences. Finally, these learners also demonstrated that (3) learners vary in their abilities to self-assess with accuracy, and individual differences in this accuracy can be accounted for with proficiency level. Implications for instruction and future research are discussed.