You can go to Yamuna Zake's website at http://www.bodylogic.com and check out all the different size balls, the book, the video etc. In fact, I don't think she will sell you any balls unless you purchase either the book or the video. Probably legal reasons...similar endangerment sites for deep tissue massage as with the body rolling (ie: over floating ribs etc). I bought the book and balls after going to the AMTA convention two years ago. She was one of the speakers. Unfortunately, I did not attend that workshop, but all my friends did and I soon wanted in on all the fun. Honestly, I don't like her writing style. A bit self-indulgent...kinda like she's just trying to fill up space to make a thicker book...but the pix are good and it's pretty intuitive stuff anyway. I hear the video is better...but if you can go to one of her workshops, do it. She is an amazing person. I ABSOLUTELY LOVE BODY-ROLLING!! I find that I've adapted it a bit for my own body...but just learning to listen to my body, feel it relax into the balls...has been really empowering for me. In two minutes of use, I corrected a two year knee problem that hasn't returned since. Check it out. Definitely.