Yes, before you paint on a canvas with acrylic paint you must apply gesso. Why? If you don't prime your canvas before painting, the paint will seep through the canvas, soaking up the paint. I had no idea until now, and it was a learning process. It took me a night, and a day to prime my canvas, wait for it to dry, and start sketching on it. I read up on how to do it on line. Some websites called it and art form in itself. Other sites just said it was simple. I guess it depends on your mind set. For me, it was not difficult to do, but time consuming. My advise is that if your are going to paint on canvas, set aside at least 24 hours to gesso your canvas before you start painting. I diluted my gesso, and then applied about three coats to the canvas because my bottle was so small. A 4 ounce bottle cost me over $10.00. Luckly when I got to class, my professor had a gallon of it and I was able to give my canvas another coat. A quick tip also, use a painters brush (at least 3 inches). This will make applying the gesso less time consuming. My brush at home was a 1 inch flat brush, and it took forever to apply just one coat. Now, to painting I go.