Jack Russell Terrier is a small, predominantly white-bodied, smooth or rough-coated terrier. This unique terrier has its beginning in fox hunting, and its working ability and its appearance has been preserved as much as it existed 200 years ago. The Jack Russell Terrier is also commonly known as Jack or JRT.

Jack Russell Terriers are sturdy and tough, and the dog should portray a compact and balanced image. With almost 50% white, and black or tan markings, they exhibit a smooth, broken or rough coat. The skin can sometimes show a pattern of small black or brown spots, which it referred to as "ticking" and this, does not carry through to the outer coat. The terrier’s tail is set high, and was in the past cropped to provide a good hand-hold grip of the terrier. Jack Russells must always appear alert and poised. As Jacks are meant to be working terriers, the most important physical attribute is their chest size, which should not be too large in order for them to enter and work in burrows.

Jack Russells tend to be extremely intelligent, athletic, fearless, and vocal dogs. It is also very normal for these dogs to become moody or destructive if they are not properly stimulated and exercised as they have a tendency to bore easily and will often create their own fun when left alone to entertain themselves. It is recommended that owners bring their Jacks for obedience classes as these terriers can be stubborn at times, and turn aggressive towards other animals and humans if not properly socialized enough. The Jacks are really energetic animals, and need lots of exercise and stimulation. Jack Russells can cohabitate with well behaved children but both dog and child need to be properly introduced and educated on how to behave towards one another. The Jack Russell is one dog that is fearless, happy, alert, confident, intelligent and lively.