<p>TDP-43 is a ubiquitously expressed, primarily nuclear DNA/RNA-binding protein implicated in neurodegenerative diseases including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer’s disease (AD). In this review, we examine the structure and regulation of TDP-43, how these features influence its localization and functional activity, and how their disruption may contribute to disease. Among TDP-43’s diverse functions, splicing repression of nonconserved RNA sequences termed cryptic exons has emerged as especially central to human disease. TDP-43 nuclear depletion and cytoplasmic aggregation are well-established pathological features in affected neurons and glia of neurodegenerative diseases, and accumulating evidence suggests that loss of TDP-43-mediated splicing repression occurs presymptomatically in disease. Advances in RNA-sequencing have enabled systematic identification of cryptic exon inclusion as a sensitive marker of TDP-43 dysfunction. Here, we synthesize current knowledge of TDP-43 biology and curate datasets from human tissues and experimental models, focusing on cryptic splicing to provide a resource for leveraging cryptic exon biology to better understand, detect, and target TDP-43 dysfunction.</p>