General: the Devon Rex is a breed of unique appearance. Its large eyes, short muzzle, prominent cheekbones, and huge, low-set ears create a characteristic elfin look. A cat of medium fine frame, the Devon is well covered with soft, wavy fur; the fur is of a distinctive texture, as the mutation which causes its wavy coat is cultivated in no other breed. Devon rex is alert and active and shows a lively interest in its surroundings.
Head: modified wedge. In the front view, the wedge is delineated by a narrowing series of three (3) distinct convex curves: outer edge of ear lobes, cheekbones, and whisker pads. Head to be broad but slightly longer than it is broad. Face to be full-cheeked with pronounced cheekbones and a whisker break. In profile, nose with a strongly marked stop; forehead curving back to a flat skull. Allowance to be made for stud jowls in the adult male.
Muzzle: short, well-developed. Prominent whisker pads.
Chin: strong, well-developed. In profile, chin shall line up vertically with nose, being neither undershot nor overshot.
Eyes: large and wide set, oval in shape, and sloping towards outer edges of ears. Any eye color is acceptable, as no points are assigned to eye color (although colorpoints generally will have blue and minks generally will have aqua eyes).
Ears: strikingly large and set very low, very wide at the base, so that the outside base of ear extends beyond the line of the wedge. Tapering to rounded tops and well covered with fine fur. With or without earmuffs and/or ear-tip tufts.
Body: hard and muscular, slender, and of medium length. Broad in chest and medium fine in boning, with medium fine but sturdy legs. Carried high on the legs with the hind legs somewhat longer than the front. Allowance to be made for larger size in males, as long as good proportions are maintained.
Legs and paws: legs long and slim. Paws small and oval, with five toes in front and four behind.
Tail: long, fine, and tapering, well covered with short fur.
Neck: medium long and slender.
Coat:
Density: the cat is well covered with fur, with the greatest density occurring on the back, sides, tail, legs, face, and ears. Slightly less density is permitted on the top of head, neck, chest, and abdomen. Bare patches are a fault in kittens and a serious fault in adults; however the existence of down on the underparts of the body should not be misinterpreted as bareness. Sparse hair on the temples (forehead in front of the ears) is not a fault.
Texture: the coat is soft, fine, full-bodied, and rexed (i.e., appearing to be without guard hairs).
Length: the coat is short on the back, sides, upper legs, and tail. It is very short on the head, ears, neck, paws, chest, and abdomen. Kittens may have very short fur all over; even if not long enough to wave, it must cover the kitten evenly, so that no bare patches are evident.
Waviness: a rippled wave effect should be apparent when the coat is smoothed with one's hand. The wave is most evident where the coat is the longest, on the body and tail.
Penalize: narrow, long, round or domestic-type head; extremely short muzzle; misaligned bite; small or high set ears; short, bare, or bushy tail; straight or shaggy coat; bare patches.
Disqualify: extensive baldness, kinked or abnormal tail, incorrect number of toes, crossed eyes, weak hind legs. Any evidence of illness or poor health.
Coat colors: any genetically possible color and pattern and any combination of genetically possible color and pattern are allowed.
Devon Rex allowable outcross breeds: no.

Point score according devon rex standard RUI:

Head (35 points):
Size and shape ___________________________________ 10 points
Muzzle and Chin __________________________________   5 points
Profile __________________________________________   5 points
Eyes ___________________________________________  5 points
Ears ____________________________________________ 10 points

Body (30 points):
Torso ___________________________________________ 10 points
Legs and paws ___________________________________  10 points
Tail _____________________________________________  5 points
Neck ____________________________________________  5 points

Coat (30 points):
Density _________________________________________ 10 points
Texture and length _________________________________10 points
Waviness ________________________________________10 points

Color (5 points):
Coat color _______________________________________ 5 points

Source: official website of feline system Rolandus Union International (RUI)