Nietzsche talks about trust [vertraue*] and mistrust [misstrau*] in all of his published and authorized works, from The Birth of Tragedy to Ecce Homo. He refers to trust in 90 passages and mistrust in 101 – approximately ten times as often as he refers to resentment/ressentiment. Yet the scholarly literature on Nietzsche and trust includes just a handful of publications. Worse still, I have been unable to find a single publication devoted to Nietzsche and mistrust. This chapter aims to fill the gap in the secondary literature by using digital humanities methods to systematically investigate the functions of trust and mistrust in Nietzsche’s writings. I argue that Nietzsche offers three main insights into trust and an additional two into mistrust. When it comes to trust, in his free spirit works, he reflects on the development of interpersonal trust, with an eye to situations in which trust is or is not reciprocated. He also criticizes some of the heuristics people use to identify trustworthy partners, especially the notion that all and only people with stable character are trustworthy. And perhaps Nietzsche’s most interesting thoughts about trust relate to self-trust, which he thinks is often unjustifiably undermined. When it comes to mistrust, although he regards generalized mistrust as a sign of bad character, he also thinks that harnessing mistrust can be valuable in at least two domains. One is morality, where we are disposed to accept traditional pieties and would benefit from turning a suspicious eye towards these pieties. The other is science, which systematizes both trust and mistrust in pursuit of the truth.