This study describes a revision of a widely used parent-report measure of infant temperament, the Infant Behavior Questionnaire (IBQ; Rothbart, 1981). A rationally derived instrument was developed that included nine new scales and minor modifications of the seven scales of the IBQ. Parents of 360 infants, equally distributed over three age groups: 3–6 months; 6–9 months; and 9–12 months of age, participated. Conceptual and item analyses provided support for 14 of the 16 proposed scales, demonstrating satisfactory internal consistency. Inter-rater reliability was evaluated, with evidence of moderate agreement between primary and secondary caregivers. Monomethod discriminant validity was demonstrated through an examination of correlations among the Infant Behavior Questionnaire—Revised (IBQ-R) scale scores. Results of the factor analytic procedure were consistent with three broad dimensions of Surgency/Extraversion, Negative Affectivity, and Orienting/Regulation. Developmental and gender differences were also noted for a number of the IBQ-R scales. Specifically, older infants received higher scores on Approach, Vocal Reactivity, High Intensity Pleasure, Activity, Perceptual Sensitivity, Distress to Limitations, and Fear, whereas younger infants’ scores were higher for Low Intensity Pleasure, Cuddliness/Affiliation, and Duration of Orienting. Male infants obtained higher scores on Activity and High Intensity Pleasure, and female infants were rated higher on the Fear scale.