PROJECT SUMMARY/ABSTRACT Only 2 in 8 young adults (age 18-30 years) with type 1 diabetes (T1D) achieve glycemic targets (A1C < 7.0%). In well-controlled lab studies sleep deprivation impairs glucose tolerance and insulin sensitivity, a reduces acute insulin response to glucose, impairs body weight regulation (lower leptin, higher ghrelin), and impairs alertness in young adults without chronic conditions and decreases insulin sensitivity in middle-aged adults with T1D. Using cognitive-behavioral approaches to sleep by 1 hour over 6 weeks to 12 months in natural environments is feasible and contributes to improvements in insulin sensitivity, glucose tolerance, and general distress symptoms in young adults without chronic conditions and improved time in glucose range in adolescents with T1D. Sleep duration, regularity, and timing are modifiable targets that may improve glycemia and other important diabetes self-management outcomes in young adults with T1D. Here we leverage our preliminary findings in the proposed study to advance cognitive-behavioral sleep self-management for T1D (K99/R00NR018886). We propose to enroll 248 young adults ages 18-30 years with T1D (50% female, 40% underrepresented) who are not achieving glycemic targets (A1C ≥ 7%). The goals of this study are two-fold: (1) to compare the immediate and short-term effects of a 3-month cognitive-behavioral sleep self-management intervention (CB-sleep) versus enhanced usual care (time-balanced attention control) on sleep health dimensions and glycemia and (2) to determine whether sleep health mediates the associations between the intervention and control condition over 9 months (baseline to 3 months and 6 and 9 months post baseline). We will randomize 1:1 to the CB-sleep or enhanced usual care condition (time balanced attention control). Sleep health dimensions will be rigorously measured using validated tools: regularity (actigraphy and self-report), satisfaction (Patient-Reported Outcomes Measurement Information System Sleep Disturbance), alertness (Epworth Sleepiness), timing, efficiency, and duration (actigraphy and self-report). Glycemia will be determined by A1C (primary outcome) with subgroup analyses of glucose variability/glucose percentage time in range 70-180 mg/dL (via continuous glucose monitors or self-monitored blood glucose six times daily). Data will be analyzed using multivariate techniques, and efficacy will be determined.