This article provides detailed protocols for creating animal models of type 1 and type 2 diabetes using streptozotocin (STZ) in mice and rats. STZ is an antibiotic that selectively destroys pancreatic islet β-cells, leading to insulin deficiency and hyperglycemia. The protocols describe the administration of multiple low doses of STZ to mice over five consecutive days, which more closely resembles the pathogenesis and morphologic changes seen in human type 1 diabetes (T1DM). This method is cost-effective and produces a model with chronic pancreatic islet inflammation, insulitis, and insulin deficiency. For rats, a single high dose of STZ (200 mg/kg) is used, which rapidly causes diabetes with blood glucose concentrations exceeding 500 mg/dl within 48 hours. The article also describes two protocols for creating animal models of type 2 diabetes (T2D) using STZ. The first model involves concurrent administration of nicotinamide to partially protect β-cells against STZ, resulting in a model of insulin-deficient but not insulin-resistant T2D. The second model involves exposing animals to a high-fat diet to induce insulin resistance followed by a moderate dose of STZ to reduce β-cell capacity, leading to hyperglycemia, hyperinsulinemia, and insulin resistance. These models are valuable for evaluating treatments for both T1DM and T2D, as they closely mimic the pathological consequences of these conditions. The article emphasizes the importance of proper animal care and handling, as well as the need for Institutional Animal Care and Use Committee (IACUC) approval for all experimental protocols.This article provides detailed protocols for creating animal models of type 1 and type 2 diabetes using streptozotocin (STZ) in mice and rats. STZ is an antibiotic that selectively destroys pancreatic islet β-cells, leading to insulin deficiency and hyperglycemia. The protocols describe the administration of multiple low doses of STZ to mice over five consecutive days, which more closely resembles the pathogenesis and morphologic changes seen in human type 1 diabetes (T1DM). This method is cost-effective and produces a model with chronic pancreatic islet inflammation, insulitis, and insulin deficiency. For rats, a single high dose of STZ (200 mg/kg) is used, which rapidly causes diabetes with blood glucose concentrations exceeding 500 mg/dl within 48 hours. The article also describes two protocols for creating animal models of type 2 diabetes (T2D) using STZ. The first model involves concurrent administration of nicotinamide to partially protect β-cells against STZ, resulting in a model of insulin-deficient but not insulin-resistant T2D. The second model involves exposing animals to a high-fat diet to induce insulin resistance followed by a moderate dose of STZ to reduce β-cell capacity, leading to hyperglycemia, hyperinsulinemia, and insulin resistance. These models are valuable for evaluating treatments for both T1DM and T2D, as they closely mimic the pathological consequences of these conditions. The article emphasizes the importance of proper animal care and handling, as well as the need for Institutional Animal Care and Use Committee (IACUC) approval for all experimental protocols.