Why it is that I see all my textures coming out sideways on faces in my model. I am using OpenGL with the following code;

glBindTexture(GL_TEXTURE_2D, Texture[Idx]);
glBegin(GL_QUADS);

glTexCoord2f(0,0);
glVertex3f(X, Y, Z);
glTexCoord2f(U, 0);
glVertex3f(X, Y, Z);
glTexCoord2f(U, V);
glVertex3f(X, Y, Z);

glEnd();

What is going on here?