Caroline Golon offers the basics of the therapy cat certification process. To train as an official cat therapy team, you need to meet minimum requirements, which vary by the certifying organization. Most programs also require that the cat be able to wear a leash and harness, mostly for the cat’s own safety.
Source: Catster, May 4, 2017.
Obviously, not all cats make good therapy cats. Animals who are calm, confident, friendly, and OK with unpredictable or new situations do well as therapy animals.