Hill's Prescription Diets are a range of clinically tailored foods that have been nutritionally blended to account for certain medical concerns. Hill's recognises that cats with health problems need a different balance of proteins, vitamins and fibres to support internal functions that are perhaps being put under strain.
Cats with problems relating to their kidneys, joints, skin, weight and digestion can all benefit from a Hill's diet that has been specially formulated to support and nourish areas of the body where it's most needed. While the Prescription Diets do not require a prescription, they should only be fed under the supervision of your vet as the differing nutrient profiles may not be suitable for all cats.
While it might be a high-end diet in terms of its price, it will probably be more economical for you in long run as your cat will need to consume less of it (compared to consuming a cheaper alternative). To learn more about this, read the related blog.
A corresponding range is also available for dogs.