hundershirt"s patent-pending design is a pressure wrap that applies a gentle, constant pressure on a dog"s torso.A survey of Thundershirt users shows that over 85% of dogs show significant improvement in at least one anxiety symptom when using Thundershirt.Thundershirt is an excellent treatment for most types of canine anxiety. For many anxieties, we recommend just putting on a Thundershirt and observing the results. No training! You very well may see significant improvement for noise, crate, travel and others with absolutely no training.For more complicated anxiety cases, we recommend using Thundershirt as part of a behavior modification program. One thing is for certain, for a very large percentage of dogs, Thundershirt"s gentle, constant pressure has a terrific calming effect. This has obvious benefits for most types of anxiety. But Thundershirt is also a very useful tool for managing excitability or hyperactivity with strangers, on the leash, or in a training environment.When selecting a size, CHEST SIZE is the most important measurement!!