Ralph Hertwig (born 4 November 1963, in Heilbronn, West Germany) is a German psychologist whose work focuses on the psychology of human judgment and decision making.

His work investigates how decision making can be modeled in terms of fast and frugal heuristics—simple cognitive strategies that use little information and rely on just a few processing steps.

In his Ph.D. dissertation, he showed that the conjunction fallacy, a seemingly logical error often illustrated by the Linda problem,[8] reflects people's capacity to infer the meaning of polysemous terms like probability.

[9][10] Another reason why fast and frugal heuristics can yield good decisions is that they take advantage of evolved cognitive capacities of the human mind.

[18] One such function is to act as an emotion-regulation device: people may avoid potentially threatening health information because it compromises cherished beliefs, they anticipate mental discomfort, or they want to keep hope alive.

For instance, a boost with proven effectiveness in improving the quality of relationships is to imagine oneself as a third-party spectator when involved in a quarrel, and to mentally engage with this perspective-shifting strategy through quick writing exercises.

[21] In an article written in collaboration with Till Grüne-Yanoff,[22] Hertwig examined how boosts differ from nudges in terms of the psychological mechanisms through which they operate, as well as their normative implications for transparency and autonomy.