Repeated behaviour is the scale at which Atomic Habits examines change. James Clear directs attention toward the systems supporting a habit as well as the outcome someone hopes to achieve. The book brings ideas from biology, psychology and neuroscience into its account of everyday actions.

Its practical subjects include motivation, environment and setbacks: making space for a new habit, arranging surroundings to support it, and returning after a routine has been interrupted. Examples from people in different fields accompany the discussion of how small behaviours accumulate.