This is the characteristics of our experience of Tibetan Mastiffs.

Our experience of our Tibetan Mastiff family has been very enlightening.
They show affection when it suits them,but when they are ready its lots of kisses and cuddles.
They are a very aloof breed. From our experience we don't have a lot of problems because there is someone in the house constantly,they need companionship. 
Our dogs are not constant barkers only when they sense something around,at the door or a car going past in the lane,then they definately let you know.
You need a sturdy high fence in the garden,because they have inherited a Steve Mcqueen great escape act. Provided they are well secured there is no problem.
We find even if you are not going to show these dogs, take them to some form of dog classes ie 
Ring craft etc. Do this from an early stage and this socialises them with other dogs and people.
One of the things we have done with our dogs since they were puppies is that we took them down to our local street market where they have a lot of attention shown to them. An hour shopping can take three hours because lots of people asking questions and showing affection to the dogs which is lovely,just remember to allow a lot more time for your shopping. 
Anybody thinking of having one of these lovely dogs we highly recommend that you buy a book called Tibetan Mastiff by Juliette Cunliffe.This will give a good insight to this breed.
(as amended 1 Nov. 2004)
This strong, well built dog is found in the foothills of the Himalayas and the borders of Tibet. He is primarily a guard dog, used to protect the flocks from preying wildlife and the home from intruders.
A powerful dog, without the massive frame of the Mastiff, he is well coated with a bushy tail. Usually, black, or black and tan, he can also be found in gold, and shades of grey. In his native environment he is very distrustful of strangers, and can be quite ferocious. However, dogs bred in Europe and America do not generally display these tendencies.
Large, powerfully built, slightly longer than high. Well boned and muscled, never light but always agile. Impressive head provides a noble, dignified look, enhanced by a mane, which is more pronounced in males, balanced by a well feathered tail carried over the back.
A loyal companion, and guardian. Slow to mature.
Independently minded, aloof and protective. Calm and patient. May be wary of strangers.
Broad, heavy and strong. Skull large, with strongly defined occiput and marked stop. Length from nose to stop equal or slightly less than length from stop to occiput. Muzzle fairly broad, well filled, blunt, and square viewed from all sides. Broad, black nose, well opened nostrils. Lips well developed with moderate flews. In maturity, some wrinkling on head extending from above eyes to corner of mouth.
Very expressive, medium size, dark brown. Set well apart oval and slightly slanting. Dark, close fitting eye rims.
Medium size, triangular, pendant, not set too low, hanging close to head. When alert, carried forward. Ear leathers covered with soft, short hair.
Jaws strong with perfect, regular and complete scissor bite, i.e. upper teeth closely overlapping lower teeth and set square to the jaws. Level bite acceptable. Full dentition desirable.
Strong, well muscled, slightly arched. Not too much dewlap.
Muscular, well laid shoulders. Strongly boned, straight legs with strong, slightly sloping pasterns.
From point of shoulder to point of buttock slightly longer than height at withers, as 10 to 9. Strong and straight back. Broad, muscular loins, with very slightly sloping croup. Chest rather deep, of moderate breadth. Ribcage oval, ribs well sprung but not barrelled, carried well back. Brisket reaching to, or just below, elbows.
Powerful, muscular, with moderate angulation and strong, low-set hocks. Hindlegs, seen from behind, parallel. Single or double dewclaws may be present.
Fairly large, strong, with thick pads, rounded and compact. Having good feathering between toes.
Medium to long. Set on high. Loosely curled over back to one side. Well feathered.
Powerful and free, with purpose and agility. Measured and deliberate when walking. At speed will tend to single-track.
Males carry noticeably more than females. Quality of greater importance than quantity. Densely coated, fairly long, thick, with heavy, woolly undercoat in cold weather which becomes rather sparse in warmer months. Hair fine, hard and straight, never silky, curly or wavy. Hair on face short. Neck and shoulders heavily coated, giving mane-like appearance. Tail heavily feathered, hindlegs well feathered on upper rear parts.
Rich black, with or without tan; slate grey, with or without tan; rich golden. The rich tan markings appear above eyes, on muzzle, on chest, the lower part of legs and underside of tail. Spectacle markings around eyes acceptable. White star on breast permissible. Minimal white markings on feet tolerated. Cream, white, chocolate/liver, parti-colour, brindle or flecked are undesirable.
A minimum height of 66 cms. (26ins) in dogs and 61 cms. (24ins) in bitches is desirable, but on no account should type be sacrificed to size alone.
Any departure from the foregoing points should be considered a fault and the seriousness with which the fault should be regarded should be in exact proportion to its degree and its effect upon the health and welfare of the dog.
Male animals should have two apparently normal testicles fully descended into the scrotum.