To this day, the exact nature of the detonation mechanism in core-collapse supernovae is still somewhat of a mystery. While numerical models are becoming ever more sophisticated, observations of the inner engine remain elusive. Electromagnetic radiation can only provide indirect information because the core is surrounded by dense stellar matter. Neutrinos and gravitational waves, on the other hand, can propagate almost unhindered through the stellar material. I will present the theoretical predictions of the gravitational waves emitted by core-collapse supernovae. The signal predictions are based on two sets of simulations carried out by the Garching group. The first set of models are simulations of the core-collapse of three non-rotating progenitors. The second set of simulations include models based on rotating stellar progenitors. The rotation rates of these initial models are motivated by realistic rotation rates obtained by stellar evolution calculations. I will summarize our current best predictions, focusing on which parts of the signals are robust and which seems more stochastic. Specific physical processes lead to distinct emission components and how we can learn about core-collapse supernovae by studying the time-frequency evolution of the gravitational waves they emit. In one of the rotating models, which explodes, a drift the central frequency of one of the signal components can be observed. I will discuss how this allows us to probe the rotation of the stellar core, which is currently not possible by any other means in the slow-rotating regime. Towards the end of my talk, I will shortly discuss the detection prospects of these models.