What are the differences between diffusion and active transport?

The key difference between these two processes is that diffusion is the movement of particles from a region of high concentration to a region of low concentration, whereas in active transport the molecules move from a region of low concentration to a region of high concentration, against the concentration gradient. Since active transport goes against the concentration gradient, it requires ATP, but this is not the case for diffusion so the movement of particles in diffusion is passive.