This thesis defends an account of what it is to trust other people, and what gives matters of trust (i.e. situations where we trust/distrust others) a characteristic interpersonal, normative, or moral/ethical importance to us. In other words, it answers what the nature of betrayal (and being susceptible to betrayal) is. -/- Along the way I put forward/defend accounts of the following: the relationship between trust and reliance (chapter 4); an account of reliance itself (chapter 5); trust and distrust as one/two/three-place (...) attitudes (chapter 7); and the ethical/normative significance of trust and betrayal as a matter of attachment security (chapters 6 and 8). -/- In addition to these accounts, the thesis also gives (in chapter 2) a conceptual/historical overview of the dominant paradigm in philosophical understanding of trust: as a form of reliance 'plus' betrayal conditions (a la Baier 1986; Holton 1994; Hawley 2014, among others). It also offers a rebuttal of that dominant paradigm in chapter 3 and 4. Furthermore, it offers an overview of how trust is understood more generally across philosophical and some social scientific/psychological literature (chapter 1). It also offers a rebuttal of the rational choice/game-theoretic understanding of trust and economic rationality a la so-called 'trust games' (chapter 1). This carries the consequence that analysis of trust in these traditions is not really based on anything resembling interpersonal trust, as we would intuitively recognise it. (shrink)