Counting significant procedural variations, there are at least 100 different animal models of fear and anxiety. Here we summarize the contribution of animal models to our current understanding of neurobiological mechanisms and discuss important distinctions such as: 1) feelings vs. defensive responding, 2) the relevance of models to fear vs. anxiety processes, 3) pharmacology- vs. neurocircuit-based models, 4) unconditioned vs. conditioned models, 5) models of state vs. trait anxiety, 6) models of fear/anxiety excitation vs. inhibition, and 6) models of normal vs. abnormal responding. We argue that models amenable to neurocircuit analysis, especially those based on threat conditioning of defensive responses, are likely to provide a deeper understanding of anxiety mechanisms and facilitate the discovery of novel treatments.