Common Rat

Native to tropical Asia (R. rattus) and China (R. norvegicus) rats had spread throughout the Old World by Roman times, and throughout the rest of the world aboard European ships in the 1500s. Here in Los Angeles we have roof rats (mostly medium gray) but in cooler parts of North America the much larger brown rat predominates (photo). The various strains of laboratory rats were developed from R. norvegicus.

While despised as filthy in the wild, rats kept as pets are found to be clean, friendly and intelligent. Most pet rats are fancier breeds of R. norvegicus. Common rat is not much cooked except in extreme circumstances because it's just not meaty enough to bother with.   Photo by Ross distributed under license Creative Commons Attribution-ShareAlike v2.0 Generic.

More on Rodents & Rabbits.

I am not aware, at this time, of anyone eating common rats except in cases of extreme hardship. Rats are commonly eaten in Asia but those are Rice Field Rats (bandicoot rats) which are much larger and meatier than even a plump R. norvegicus, never mind R. rattus. They are also safer and more consistent because you know what they've been eating.

Health & Nutrition

Rats are notorious carriers of disease, but highly adaptable and impossible to exterminate. The blood anticoagulant warfarin was thought to be the end of rats but is now being incorporated by some rats as a nutrient. R. rattus was probably the main spreader of plague and typhus in Europe, but here in Los Angeles County these diseases are rarely found associated with rats because the necessary flea vector (Xenopsylla cheopis) is seldom found on them.

Eating wild rats in North America cannot be recommended in any case because of the many eradication programs that use powerful poisons.