There are differences between a therapy dog and a service dog, but the two are often confused.
That’s why I really liked this graphic, produced by the Las Vegas Sun:

The difference between a therapy pet and a service animal (courtesy of the Las Vegas Sun)
The newspaper interviewed Sue Grundfest, Lead Animal Therapist at Southern Hills Hospital and Medical Center, for its article.
Kathleen Crisley, specialist in dog massage, rehabilitation and nutrition/food therapy, The Balanced Dog, Christchurch, New Zealand