Diabetes mellitus (DM) is a common disease estimated to affect 1 in 300 dogs presenting to veterinary clinics. Like people with type 1 DM, dogs require life-long treatment with insulin injections, and regular monitoring of glucose concentrations is imperative to successful management. Traditionally, glycemic control has been measured by performing blood glucose curves in which capillary or peripheral blood glucose is measured every 2 hours for 8-12 hours with a glucometer. More recently, flash glucose monitoring systems (FGMS) have been used to measure interstitial glucose every few minutes for up to 14 days, providing substantially more measurements with less morbidity and stress for patients and their families. The FreeStyle Libre is the most well-studied and utilized FGMS in dogs. The newest Libre 3 model is 70% smaller and requires less time and effort for users than previous models. The accuracy of the Libre 3 in dogs, however, remains unknown. This study aims to recruit 30 diabetic dogs (1) to measure the analytical and clinical accuracy of the Libre 3 FGMS compared to a glucometer and reference analyzer using 360 paired interstitial and blood glucose measurements collected over two 8-12 hour BGCs with analysis of Bland-Altman difference plots and Parke’s error grid analysis, (2) to measure the concordance between hypothetical insulin dosing recommendations and detection of hypoglycemic episodes with data provided by the Libre 3 FGMS and glucometer, and (3) to evaluate clients’ perspectives of the practical use of the Libre 3 FGMS with a questionnaire. Our primary hypothesis is that the Libre 3 FGMS has sufficient analytical and clinical accuracy to measure glycemic control and guide treatment decisions in dogs. A secondary hypothesis is that clients will find using the Libre 3 FGMS practical for monitoring glycemic control in their diabetic dogs. Validating this Libre 3 FGMS could reduce technological barriers to monitoring glycemic control with a FGMS, thereby improving the quality of life for families of diabetic dogs. In the research setting, Libre 3 may allow for more glucose measurements compared to previously validated models, improving the ability to detect hypoglycemic episodes and glycemic excursions in studies of novel therapies or disease models in which it is vital to perform serial glucose monitoring.