Selection is weak, so evolutionary change is slow. That's the classical picture. But over the last 25 years we've learned that it's often very wrong, and ecologically important traits can change markedly in just a few generations. I will talk about experimental work using aquatic predator-prey microcosms as a model system to study rapid evolution; general theory motivated by those experiments; and methods that we have been developing to apply these ideas to field data, to quantify the importance of evolutionary change and non-heritable trait changes for ecological dynamics. This is joint work with many colleagues, postdocs, and students.