Kidney disease is one of the most prevalent disease states in cats and dogs, especially in the senior and geriatric populations. The presence of worsening kidney function can affect the way that other chronic diseases (such as arthritis, thyroid disease, and metabolic diseases) are treated. This module explains the importance of early identification of decline in kidney function through preventive care and sick care, as well as in preanesthetic testing situations. The module also illustrates how to perform a complete evaluation of renal function and determine the best care protocols for patients.