This is a non-randomized, single arm, multi-center, prospective, non-significant risk study to evaluate the FreeStyle Libre Flash Glucose Monitoring System.

Up to 150 subjects will be enrolled at four (4) clinical research sites in the United States. Subjects will wear two Sensors of three unique sensor lots. Each Sensor will have a paired Reader that will be given to the subject. All Readers will be masked during the study (i.e. subjects will not be able to view glucose results obtained from the Sensor on the Reader screen). Subjects will be asked to perform at least 8 capillary Blood Glucose (BG) tests per day using the primary Reader. Interstitial glucose readings from each Sensor will be obtained with the corresponding Readers immediately following each BG test. Subjects will be instructed to report any problems with the device. Subjects will make eight (8) scheduled visits to the clinical study site, including the Enrollment/Screening Visit (Visit 1). Subjects will have five (5) in-clinic visits during which intravenous blood draws and YSI reference testing will occur.

Inclusion Criteria:

• Subject must be at least 18 years of age.
• Subject must have type 1 or type 2 diabetes.
• Subject must require insulin therapy through an insulin pump and/or multiple daily insulin injections (at least 3 injections daily).
• Willing to perform a minimum of 8 finger sticks per day during the study.
• Subject must be willing to fast five individual times prior to in-clinic visits, each fast lasting a minimum of eight hours.
• Subject must be able to read and understand English.
• In the investigator's opinion, the subject must be able to follow the instructions provided to him/her by the study site and perform all study tasks as specified by the protocol.
• Subject must be available to participate in all study visits.
• Subject must be willing and able to provide written signed and dated informed consent.

Exclusion Criteria:

• Subject has known allergy to medical grade adhesive or isopropyl alcohol used to disinfect skin.
• Subject is pregnant, attempting to conceive or not willing and able to practice birth control during the study duration (applicable to female subjects only).
• Subject has extensive skin changes/diseases at the proposed application sites that could interfere with device placement or the accuracy of interstitial glucose measurements. Such conditions include, but are not limited to extensive psoriasis, recent burns or severe sunburn, extensive eczema, extensive scarring, dermatitis herpetiformis, skin lesions, redness, infection or edema.
• Subject is currently participating in another clinical trial.
• Subject has donated blood within 112 days (3.7 months) prior to the beginning of the study activities.
• Subject is anemic as determined by the Investigator.
• Subject has concomitant medical condition which, in the opinion of the investigator, could interfere with the study or present a risk to the safety or welfare of the subject or study staff. Such conditions include but are not limited to History of HIV, Hepatitis B or C.
• Subject has X-ray, MRI or CT appointment scheduled during the period of study participation, and the appointment cannot be rescheduled for a time before study participation starts or after study participation ends.
• Subject is unsuitable for participation due to any other cause as determined by the Investigator.

Subjects with type 1 or type 2 diabetes requiring multiple daily insulin injections (MDI) or continuous subcutaneous insulin infusion (CSII).