In this thesis, I explore motivational internalism and externalism, which concern the relationship between moral judgments and motivation. I first introduce the basic terms and different forms of internalism and externalism, including the externalist objections to internalism based on the famous counterexamples. I then argue against externalism by defending and developing Michael Smith’s fetishism argument. I not only respond to the externalist objections to the fetishism argument but also further argue against different externalist explanations of moral motivation that intend to (...) avoid the fetishism charge. Finally, I re-examine different forms of internalism in order to argue for a new form of internalism that can better preserve our internalist intuitions whilst accommodating the externalist counterexamples. My ultimate conclusion will be that the most plausible form of internalism to accept is constitutional, unconditional, relatively strong, direct internalism that is formulated in terms of dispositional desires. (shrink)