Collision detection is a crucial component of any game, simulation, or interactive application. Greenfoot provides built-in methods of detecting collisions. In this chapter, we carefully explained each of these methods and then demonstrated how you could use them to do more advanced collision detection. Specifically, we discussed border-based and hidden-sprite techniques. Moving forward, we will use collision detection often and will choose a method appropriate for our example. In the next chapter, we will look at projectiles and will have ample opportunity to put into practice what you have learned in this chapter.