As birders we may think that we all know what we mean when we talk about species, and in the field of biology there are few ideas that impinge on more research than the concept of species. Species are the currency with which we do our studies as biologists and they are the currency of our birding life lists as well. Species are how we convey what we learn as biologists and what we see as birders. We also have laws enacted that protect species. Yet, it turns out that defining species isn't all that simple, and that there are innumerable ways to define species, and that these different concepts have different utilities as well. Some of the changes that you see to your life list through lumping and splitting are in part due to different definitions and philosophies being applied to understand and describe avian biodiversity. Jason Weckstein, Associate Curator of Ornithology at the Academy of Natural Sciences of Drexel University, will talk about species concepts, what are they, how do they differ in their utility, some examples of how they are applied, and what they tell us about the birds that we all love.