Inclusion Criteria:

• Clinical diagnosis of type 1 diabetes and using daily insulin therapy for at least one year

  • The diagnosis of type 1 diabetes is based on the investigator's judgment; C peptide level and antibody determinations are not needed.
• Age >8 years

• Glycated hemoglobin(HbA1c) 7.0%-10.0% for the primary cohort and <7.0% for the secondary cohort

  • The DCA2000 or comparable point of care device will be used to assess eligibility.

• Insulin regimen involves either use of an insulin pump or multiple daily injections of insulin (at least 3 shots per day) and has been stable for the last two months, with no plans to switch the modality of insulin administration during the next 6 months (e.g., injection user switching to a pump, pump user switching to injections, or the addition of Lantus (Glargine) insulin)

  • Subjects using premixed fixed doses of insulin at the time of enrollment will not be eligible
• Subject (and parent/guardian for children) understands the study protocol and agrees to comply with it

• Subjects >9 years old and primary care giver (i.e., parent or guardian if subject is a minor) comprehend written English or Spanish

  • This requirement is due to the fact that the questionnaires to be used as outcome measures do not have validated versions in other languages.
  • Spanish-speaking subjects will be enrolled only if a RT-CGM device that functions in Spanish and has a User Guide in Spanish is available.
• No expectation that subject will be moving out of the area of the clinical center during the next year, unless the move will be to an area served by another study center.
• Informed Consent Form signed by the subject (or parent/guardian if subject is a minor, with subject signing the Child Assent Form)

Exclusion Criteria:

• The presence of a significant medical disorder or use of a medication such as oral/inhaled glucocorticoids that in the judgment of the investigator will affect the wearing of the sensors or the completion of any aspect of the protocol.

• The presence of any of the following diseases:

  • Asthma if treated with systemic or inhaled corticosteroids in the last 6 months
  • Cystic fibrosis
• Adequately treated thyroid disease and celiac disease do not exclude subjects from enrollment
• Inpatient psychiatric treatment in the past 6 months (if the subject is a minor, for either the subject or the subject's primary care giver).

• Home use of RT-CGM in past 6 months

  • Use of a CGMS or GlucoWatch does not exclude subjects from enrollment
• Participation in an intervention study (including psychological studies) in past 6 weeks.
• Another member of the same household is participating in this study.
• For females, pregnant or intending to become pregnant during the next year Pregnancy is an exclusion because of uncertainty about the lag between interstitial fluid glucose and blood glucose during pregnancy, which might affect the accuracy of the sensor. Subjects who become pregnant during the study will be discontinued from the study.