What is Ian Malcolm's professional field in Jurassic Park?

Ian Malcolm's professional field in Jurassic Park is mathematics.

Malcolm is a fictional mathematician who specializes in chaos theory, the study of systems that can behave unpredictably even when governed by definite rules. In Michael Crichton's novel and Steven Spielberg's film, he uses that perspective to challenge John Hammond's confidence that a dinosaur park can be completely controlled.

His warnings are not merely general pessimism. Malcolm argues that complex biological systems contain too many interacting variables for engineers to predict every outcome. The park's security failure, dinosaur reproduction, and animal escapes make his chaos-theory objections dramatically relevant. Jeff Goldblum's performance helped make the character one of the franchise's most recognizable figures.

A common mix-up is calling Malcolm a biologist or paleontologist because he discusses dinosaurs. Those are different specialties: Alan Grant is the paleontologist, while Ellie Sattler is a paleobotanist. Malcolm's field is mathematics, specifically chaos theory, and the sequel identifies him as the central expert on that subject.