Hi Amzie, it is by Tony Horton who is an American personal trainer. It is a 90day high intense extreme home workout regime. It is absolutely amazing if you have the time and effort to put into it, I was seeing results within the first week! The weight loss, toning up, improved fitness and muscle definition really does speak for itself and think my pictures do too.
You can buy it on-line, you get 12 dvds along with the workout plan and diet plan (I never followed the diet)
I would recommend it to anyone. I was really unfit when I started it and the regime is tough, I managed to get to day 60 then fell ill and am starting to build up my fitness now so that I can get back to p90x again. You should give it a go
xx