Inbreeding is the mating of very close relatives, for example, father to daughter, half-brother to half-sister, brother to sister, mother to son, etc.
Inbreeding intensifies the faults as well as the strong points, so considerable discretion must be used in the choice of the dogs. The faults may be to such an extent, that, sometimes, entire litters have to be destroyed in cases where obvious anomalies occur. For this reason, this type of breeding is not recommended to novice breeders.
Sometimes, in-breeding is the only option available, for example, in the re-creation of a nearly extinct breed or in breeding programs of newly created breeds.
Line breeding is the mating of dogs having many common ancestors or mating to a slightly removed relative, e.g. granddaughter to grandsire, uncle to niece, etc.
The benefit of line-breeding is the production of more consistent litters.
In order to have a chance to reinforce desired characteristics and eliminate health problems one has to have a thorough knowledge of both pedigrees of both the sire and the dam for at least five generations.
In general, most breeders adhere to a policy of line breeding, whereby they can assure uniformity of quality without risking the inherent dangers of inbreeding.
This technique appears to be the best compromise between inbreeding and the doubts of outcrossing or outbreeding.
Outcrossing is the mating of two dogs that are the products of line breeding but of two distinctly separate lines.
Unless the two dogs involved in an outcross are strongly linebred with a possibility of a certain measure of prepotency, uniformity to the first generation is generally doubtful.
It is generally employed as a long-term proposition to bring certain traits into a line that are otherwise deficient. These traits then need to be intensified by proper line breeding or inbreeding.
Outbreeding is the mating of two dogs who not only are the products of two distinctly separate lines, but on top are not the products of line breeding.
Outbreeding is seldom employed since in most breeding programs dogs that would qualify for outbreeding simply do not exist.
In summary, most successful breeders use some formula involving general line breeding with inbreeding employed when sufficiently outstanding products of their line result and outcrossing only when another line can supply a strong characteristic in which they are lacking.