All gravitational systems can create gravitational waves. However, gravitational waves are very weak. Even Einstein believed it would be nearly impossible to detect these waves. Therefore, the events we look for are the events that make the strongest gravitational waves in the universe. These events are things like compact binary coalescences, such as merging black holes or neutron stars, exploding stars such as supernovas, fast-spinning neutron stars like pulsars, or the leftover gravitational wave background from the big bang. Even more exciting than these already fascinating events is the possibility of the unexpected. Exotic predictions like cosmic strings, dark matter, or something that we haven't even predicted could create a gravitational wave.