The explosion of the Internet and prominence of social media platforms have created a dynamic online information ecosystem. The roles of traditional gatekeepers of credible information (e.g., news organizations) have been diminished, and individuals are often on their own in evaluating an abundance of information online coming from more sources than ever before. As a result, misinformation can easily spread in the online environment. The spread of misinformation can lead to individuals making decisions that are not in the best interests of themselves or the public, and can impact society through increasing cynicism, apathy, and extremism. To combat misinformation, individuals need to develop sufficient skills in online credibility assessment -- the ability to assess the credibility of online information and resources. Assessing the credibility of information, however, has been shown to be a difficult and complicated task in the online environment. This dissertation includes three interrelated studies to address the problem of the spread of misinformation in the complex online environment. These studies address this problem through a focus on a metacognitive approach to developing credibility assessment skills in individuals. First, a systematic review of literature was conducted on the intersection of metacognition and credibility assessment. This study conceptualized the roles that metacognition can play in credibility assessment and discussed how metacognition has been incorporated into credibility assessment instruction in the past. The second study documented all stages of the design and development process involved in creating an online, multimedia instructional module that applies a metacognitive approach to foster credibility assessment skills in undergraduate learners. Analysis techniques, instructional design models and frameworks, and evaluation strategies that were integral to the design process are discussed. Finally, an experimental study evaluated this online module and explored the influence of metacognitive prompting on undergraduate learners' credibility assessment abilities, behaviors, and perceptions. Metacognitive prompting was not found to lead to significant differences between groups, but analysis of quantitative and qualitative data provided valuable insights regarding the metacognitive approach to credibility assessment instruction and its impact on performance and behaviors. Findings for each study, key takeaways, and implications on research and practice are discussed. [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.]