Over the past few decades, standards-based educational reforms in the U.S. have sought to enhance students' college and career readiness. The most recent wave of such reforms has emphasized writing as an essential aspect of college readiness and a 21st century skill necessary for success in the workplace. A common feature of these conversations concerning college writing readiness is a prevailing sense that high school graduates are underprepared for postsecondary literacy demands and, relatedly, that standards-based instruction is the key to bridging this "gap." Compared to the number of studies that focus on writing at either the secondary or postsecondary level, however, few studies inquire into the nature of this transition, that is, what it means move from writing in high school to writing in college. This study, therefore, takes up this question by focusing on how first-year college writers perceive and make sense of this writing transition. The study uses a multiple case study approach of nine students enrolled in a required first-year composition (FYC) course at a four-year public university and explores how students' conceptions of writing mediate their transition experiences, including how their perceptions of previous school-based writing instruction impact the nature of these transitions. Data sources include a series of three interviews with each student, student writing samples from both high school and college, observations of participants' FYC classes, and classroom artifacts from FYC. Three key findings emerged in response to my research questions. These findings included the following: (1) to varying degrees, students tended to experience this transition as a liminal space, in that they navigated destabilizing situations as writers, ambiguous identities, and reconceptualizations of writing; (2) three sets of factors (i.e., prior and current writing instruction, writerly identities, and schooling contexts) mediated students' transitions in diverse ways and impacted the degree to which they reconceptualized writing; and (3) when it emerged as a prominent feature of their transition, these reconceptualizations of writing generally involved a shift from form-based writing to writing based on rhetorical purpose, a shift from thinking of writing as reporting to writing as inquiry, and a reconsideration of the author's point of view in various genres. The findings have implications for how we understand college writing readiness and writing development across high school to college transitions. In particular, this study suggests that reductive/formulaic conceptions of writing contribute to transition struggles and that mismatch between instructors' conceptions of writing and those of their students can exacerbate these struggles. This implication contradicts conventional wisdom that would assume that struggle is the result of skills-related deficiencies in students. The implications also shed light on the various factors that influence the nature of these transitions and the kinds of instructional approaches and pedagogies that support writing development as students move from secondary to postsecondary writing contexts. [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.]