Any sequence of radio frequency (RF) pulse forms echoes, such as spin echoes or stimulated echoes. This lecture will cover the underlying principles of such echoes. I will discuss why and when echoes occur, provide an understanding of how “to generate, recognize, use or avoid them,” to use Juergen Hennig’s words. To this end, I will explain two helpful and mutually related tools to simulate echoes: Bloch simulations and the extended phase graph formalism. Last, but not least, I will give some practical examples of how echoes are used in routine MR imaging.