In the eighteenth century, Daniel Bernoulli, Adam Smith and Jeremy Bentham proposed that economic choices rely on the computation and comparison of subjective values(1). This hypothesis continues to inform modern economic theory(2) and research in behavioural economics(3), but behavioural measures are ultimately not sufficient to verify the proposal(4). Consistent with the hypothesis, when agents make choices, neurons in the orbitofrontal cortex (OFC) encode the subjective value of offered and chosen goods(5). Value-encoding cells integrate multiple dimensions(6-9), variability in the activity of each cell group correlates with variability in choices(10,11) and the population dynamics suggests the formation of a decision(12). However, it is unclear whether these neural processes are causally related to choices. More generally, the evidence linking economic choices to value signals in the brain(13-15) remains correlational(16). Here we show that neuronal activity in the OFC is causal to economic choices. We conducted two experiments using electrical stimulation in rhesus monkeys (Macaca mulatta). Low-current stimulation increased the subjective value of individual offers and thus predictably biased choices. Conversely, high-current stimulation disrupted both the computation and the comparison of subjective values, and thus increased choice variability. These results demonstrate a causal chain linking subjective values encoded in OFC to valuation and choice. Direct electrical stimulation of the brain in rhesus monkeys (Macaca mulatta) predictably varied subjective valuation and choices, linking valuation and economic decision making to the orbitofrontal cortex.