The purpose of this study is to characterize the Freestyle Libre Flash Glucose Monitoring System performance with respect to YSI reference venous plasma sample measurements.

Up to 200 subjects will be enrolled in this study at a total of 6 clinical research sites in the United States. Subjects will wear a total of two (2) sensors, one on the back of each upper arm. 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 six (6) scheduled visits to the clinical study site, including the Enrollment/Screening Visit (Visit 1). Subjects will have three (3) 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 while wearing the sensor in the study.
• Subject must be able to read and understand English.
• Willing to have their blood sugar manipulated during in-clinic sessions.
• 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.
• At the time of enrollment, subject must be available to participate in all study visits.
• Subject must be willing and able to provide written signed and dated informed consent.
• Additional criteria for hypoglycemia induction.
• Known insulin sensitivity factor.

Exclusion Criteria:

• Subject has a history of hypoglycemia unawareness.
• 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 has had an episode of severe hypoglycemia requiring intervention from a health care professional (i.e. EMT assistance, emergency room visit, or hospital admission) within the last three (3) months.
• 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 has both hemoglobin (Hb) and hematocrit levels that are 10% or more below the normal ranges (For reference low end of the normal range for Hb for males is 14 g/dL and for females is 12 g/dL; low end of the normal hematocrit is 40% for men and 36% for women).
• Subject has concomitant medical condition which, in the opinion of the investigator, could 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, CT or diathermy 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).