This paper experimentally isolates the impact of various combinations of the following motives on trustworthiness: (i) unconditional other-regarding preferences; (ii) vulnerability-responsiveness; (iii) deal-responsiveness; and (iv) gift-responsiveness. Our results indicate that – besides unconditional other-regarding preferences like altruism and inequality aversion – vulnerability-responsiveness is the most important driver for trustworthiness. Prompted by our experimental findings we provide behavioral definitions of trust, trustworthiness, and trust-responsiveness based on revealed willingness to accept vulnerability and the response to it. An important difference from existing definitions is that ours allow trust to be present without generosity.