Diabetes mellitus is defined as a group of metabolic diseases characterized by hyperglycemia resulting from defects in insulin secretion from the pancreatic beta cells; resistance to insulin action at the level of skeletal muscle, liver, and fat; or both. The resultant hyperglycemia, if untreated, can lead to long-term vascular complications. Thirty million people in the United States are diagnosed with diabetes, and that number is expected to increase to 39 million people by 2050. Thus, millions of people require glucose-lowering therapies to maintain normal glucose levels (normoglycemia) and prevent diabetes complications. Type 1 diabetes, which accounts for 5 to 10 percent of all diabetes cases, is characterized by insulin deficiency and a need for daily insulin administration to sustain life, maintain normoglycemia, and maintain normal body weight and promote normal growth and development in children. Type 2 diabetes, which accounts for 90 to 95 percent of diabetes in the United States, is the result of a combination of insulin resistance and impaired insulin secretion by the beta cells of the endocrine pancreas. Eventually, beta cell failure can lead to insulin deficiency, necessitating insulin therapy. In pregnant women with pre-existing type 1 or type 2 diabetes, poor glycemic control is associated with poorer pregnancy outcomes. The objective of our comprehensive systematic review was to address the question of whether the mode of intensive insulin therapy (CSII vs. MDI) results in better glycemic control, less hypoglycemia, improved quality of life, and improved clinical outcomes in individuals with type 1 diabetes, type 2 diabetes, and pre-existing diabetes in pregnancy. We also sought to determine whether these outcomes differed by the type of strategy used for blood glucose monitoring (rt-CGM vs. SMBG) in those same populations. Key Questions include: KQ1. In patients receiving intensive insulin therapy, does mode of delivery (CSII vs. MDI) have a differential effect on process measures, intermediate outcomes, and clinical outcomes in patients with diabetes mellitus? Do these effects differ by: a. Type 1 or type 2 diabetes status? b. Age: very young children, adolescents, and adults, including older adults (age >65 years)? c. Pregnancy status: pre-existing type 1 or type 2 diabetes? KQ2. In patients using intensive insulin therapy (MDI or CSII), does the type of glucose monitoring (rt-CGM vs. SMBG) have a differential effect on process measures, intermediate outcomes, and clinical outcomes in patients with diabetes mellitus (i.e., what is the incremental benefit of rt-CGM in patients already using intensive insulin therapy)? Do these effects differ by: a. Type 1 or type 2 diabetes status? b. Age: very young children, adolescents, and adults, including older adults (age greater than 65 years)? c. Pregnancy status: pre-existing type 1 or type 2 diabetes? d. Intensive insulin delivery: MDI or CSII?