The JDRF CGM Study Group trial is a randomized, parallel group, efficacy and safety study. Subjects with T1DM who meet eligibility criteria are randomized to either standard self-monitoring of blood glucose (SMBG) alone or use of any of the three current RT-CGM systems as a supplement to SMBG. After the 6-month randomized period, the Control Group is offered use of RT-CGM, and both groups are studied for an additional 6 months. Subjects are divided into two cohorts: the Main Study Cohort includes subjects with baseline glycosylated hemoglobin (HbA1c) -% inclusive, and the Exploratory Pilot Study Cohort includes subjects with HbA1c<%. Difference in HbA1c is the primary outcome in the Main Study. Other outcomes include the percentage of sensor glucose values within the 70-180 mg/dL range, scores on questionnaires that assess the impact of RT-CGM on living with T1D, and the cost-effectiveness of RT-CGM.