Heritable personality traits often predict fundamental philosophical disagreement. This conclusion is based on studies of more than 15,000 people sampled from diverse cultures and educational backgrounds, including verifiable experts. In this chapter, we review some of this research showing links between personality and philosophical bias in free will, intentional action, and ethics. Our discussion focuses on serious challenges that these philosophical biases pose (e.g., limits on the use of philosophical intuitions as evidence). We close with discussion of the Philosophical Personality (...) Argument and brief consideration of emerging projects in applied experimental philosophy. (shrink)