Hi, Here's what I want to do. I create bounding box that are at various level in a quad tree. I want to extract the the planes of the frustum and test if a bounding box is inside the frustum or not. Currently, I don't care about the near and far plane. So, if a bounding box is inside the frustum, I continue to explore the quad tree. And so on until I reached a leaf and I draw what is necessary. My problem is to extract the for basic planes. I took a look at some web pages, and they use the matrix on top of the ModelView multiplied by the matrix on top of the Projection. Then, apparently, the left plane is [m14+m11, m24+m21, m34+m31, m44+m41]. I made some test with that, even by using clipping plane instead, and to help me, if a bounding box is not accepted, I draw the bounding box instead of the contain. But the problem is that I can see some bounding box that I shouldn't see. To create the plane, I extract the normal and I take the closest point to the origin. Then, I use this to test the distance of every corner of the bounding box, if one of them is on the right side of the plane, I consider the bounding box to be inside. But the problem is that I can see some rejected bounding box. I also made some test with clipping planes but these looks like they work fine. So, what am I doing wrong ?