In this issue ofVeterinary Clinics: Small Animal Practice, guest editor Dr. Stephen D. Cole brings his considerable expertise to the topic ofCanine and Feline Infectious Diseases . Top experts offer an in-depth exploration of infectious diseases affecting dogs and cats, covering all major pathogen groups (viral, bacterial, fungal, and parasitic). This issue addresses how climate change and other human factors are reshaping disease ecology, influencing pathogen distribution, and increasing the risk of vector-borne, fungal, and parasitic infections in new geographic regions. It also describes the strengths and weaknesses of new diagnostic technologies, novel therapeutic strategies, and more.