As college biology educators we want students learning how to conduct their own scientific investigations. This means designing laboratory curricula in which students exercise control and responsibility over the knowledge building actions of an investigation--that is, in which they exercise "epistemic agency." Our current understanding of epistemic agency in college biology labs is limited--we lack evidence for when, why, or how students contribute to knowledge building when conducting their own investigations, and what is the role of the curriculum in facilitating students' investigative decision making. In this dissertation I begin to fill this gap through three case studies of students in an introductory college biology lab course that employed a "hybrid lab" design--in which students controlled the production of data through experimentation with organisms and simulation with computer models. With each study I unpack when, why, or how students exercised epistemic agency in the lab, and examine the role of the lab design in facilitating these dynamics. Through accounting for student activity in these empirical studies I build theory for studying student agency, and develop design ideas for supporting students carrying out their own scientific investigations in introductory college biology labs. [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.]