Sensory systems have evolved to deal with complex and seemingly infinite sensory information. However, during evolution the morphology and neural circuitry of sensory organs have become "matched filters" for the characteristics of the most ecologically crucial stimuli that need to be detected, suppressing or even rejecting other less important stimuli. Not only do these matched filters allow essential sensory stimuli to be rapidly and reliably extracted for further processing, they do so with the most efficient use of the animal's limited energy supply. The collection of chapters in this book explore these principles across the senses, in both vertebrates and invertebrates, with a rich smorgasbord of case studies that explain how matched sensory filters are an essential feature in the ecology of animal sensing.