The purpose of this phenomenological study is to investigate the impact of instructional design elements on cognitive load for adult neurodiverse learners in online learning environments. For the utility of this study, cognitive load will be generally defined as the working memory and mental resources needed to perform a task. This study is grounded on Cognitive Load Theory (CLT) and how the cognitive load of neurodiverse learners is affected by instructional design. This study employed a qualitative thematic analysis using secondary data consisting of focus group interviews of 12 adult neurodiverse learners. This study investigated the central research question: How do neurodiverse adult learners perceive the concept of cognitive load in the context of online learning? MAXQDA was utilized to code the transcripts, with five main codes and 40 subcodes emerged. From these, five main themes emerged: cognitive load awareness, challenges in online learning, coping strategies, preferred learning styles, and recommendations for improvement. Findings indicated that ND adult learners perceive the concept of cognitive load in the context of online learning as the mental effort required to learn, process, and understand learning. Challenges in online learning for ND adult learners present as high volumes of information, course organization, operational barriers, and interaction issues as elements that contribute most significantly to cognitive load in online learning. Recommendations for future improvement in online courses include informing learners of assessed content specification, multimedia integration, accessibility features, and allowing time for breaks. [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.]