Feline Giardia infection can be subclinical, but the most common clinical symptom is diarrhea. Historically, Giardia infection was diagnosed by microscopic examination of feces, but immunological tests to detect antigens in stool are now widely used as bedside tests. However, even with improved diagnostic tools, giardia infection in cats remains a conundrum because treatment is not always 100% effective, reinfection is common, and concerns remain about the potential for zoonotic diseases.