UKCI (Universal Kennel Club International) was the first registry to recognize the Rat Terrier as a purebred and accept them as a recognized Purebred breed in 1936.

The Rat Terrier is a well known farm dog as far back as anybody can remember but their numbers started dwindling in the 1950's when modernization of farms turned more to chemical/poison varmint control thus the need for less varmint type dogs.  A few breeders still had small packs of these wonderful dogs but the gene pool was declining to very small numbers.  In an attempt to revitalize the dog and it's numbers the crossing of these dogs with the Toy Fox, Chihuahua, I.G. and  Beagle breeds was acceptable practice from the '70's until January 1, 1998 when UKCI officially refused to register any dog as a Rat Terrier that was not bred from 2 previously registered Rat Terriers.

The introduction of the Toy Fox, Chihuahua and Manchester Terrier into the bloodlines gave the smaller size that many desired for a smaller dog needed for hunting of small prey. The Rat Terrier is a tenacious squirrel dog and some say can do the job of finding, killing, retrieving and bringing home the kill all by themselves.
The introduction of the Chihuahua and Italian Greyhound gave the breed the multitude of colors that it enjoys today including the merle pattern.
The introduction of the beagle was done to hone hunting instincts but served little other purpose.
It only takes watching this vivacious little dog in it's determined attempt to retrieve it's prey to see that it's hunting instincts are very much intact today. A rat stands little if any chance against a determined Rat Terrier of any size.

This little dog may have started out being developed as a small type hunting dog but it has evolved into a dog of many purposes. It is as at home in somebody's bed as it is in the woods. It is as happy in somebody's lap as it is in the back yard. It's heart may be small in comparison to larger breeds but NO dog can be any more loyal.

The Rat Terrier made a huge come-back and gained the publics eye in the 1990's and with the popularity came the "WILL OF OTHERS" to change things to their own liking.  Breed standards that had served the Rat Terrier breed well for over 50 years started being scrutinized, argued over and changed.  One change was in the acceptable patterns.  Merle and Brindle became an overnight disqualification in some registries.  Colors and Patterns were hashed over from one end of the United States to the other and eventually the "POWERS THAT BE" got their way and most breed standards across the nation were changed to their will.  2 registries stand out for their courage and knowledge in not allowing a few to change the standard for us all and those 2 are ACR - American Canine Registry and APRI - American Pet Registry Inc.  who stood their ground and refused to eliminate things in the breed standard that was certain to once again reduce the Rat Terriers numbers and gene pool and without doubt would be unfair to the breeders who were already registering with them.

The UKCI adopted the National Rat Terrier Association's (NRTA) standard of the Rat Terrier and that is the standard that all UKCI registered Rat Terriers should be judged by.
The ACR adopted the Rat Terrier Club International standard of the Rat Terrier and that is the standard that all ACR registered Rat Terriers should be judged by.
Keep in mind here though that several registries now accept the Rat Terrier as a recognized breed for registration and each Registry carries their own set of standards according to their breed clubs standards.

Registries that are most prevalent in promoting the Rat Terrier as a purebred are ACR (American Canine Registry), UKCI (Universal Kennel Club), APRI (America's Pet Registry Inc.) and UKC (United Kennel Club).
Other registries do register the Rat Terrier as a breed but their registration policies are less stringent than the ones above therefore making me question the PUREBRED status of such puppies/dogs.
There was rumor in 2001 that AKC (American Kennel Club) was to accept Rat Terriers for foundation stock into their registry. This would be a happy/sad occasion for the Rat Terrier as a breed. It would mean that one of the largest registries in the world has finally accepted the Rat Terrier as a breed probably due to it's increasing large number of breeders and pups being produced but it could also mean the loss of health of our beloved Rat Terrier. Show Breeders have a tendency to continually breed back to related dogs which can give them a superior show dog but can also give them less vigor, more health problems and will surely start to change the looks of the dog that we so love as it is now.   The rumor was indeed true and AKC now does FSS Foundation Status Registration of the Rat Terrier.  Once the database has been built to a sufficient number they will be recognized as a full AKC breed.

While the RTCA tries to make it seem that they were the official breed standard producers of an accepted breed standard that could be nothing further from the truth as UKCI did and does to this day have a recognized breed standard long before RTCA was even a dream.

Many try to accredit UKC (*UNITED) as being the first registry of Rat Terriers and again this is nothing but untruth.  UKCI (*UNIVERSAL) was the first REGISTRY to recognize and REGISTER the Rat Terrier.  A registry is nothing but a company who DOCUMENTS and ISSUES paperwork and that is EXACTLY what UKCI has been doing with the Rat Terriers since 1936 which is a far cry longer than UKC's acceptance and documentation of the breed in 1999.