Evaluation of the probability of success is an important task when selecting patients for psychotherapy. Discussions of selection criteria for psychotherapy often focus on variables that reflect the patient's “readiness.” Readiness refers to the patient's positive attitude and preparedness to enter into a therapeutic relationship for the purpose of resolving problems. Although the concept of readiness is generally regarded as highly important, no widely accepted measure of it exists. The objective of the present study was to develop an efficient yet comprehensive measure of readiness for psychotherapy, called the Readiness for Psychotherapy Index (RPI). The study resulted in a 20-item scale that assessed 4 aspects of readiness. All 4 factors had high internal consistencies (≥0.70). We found evidence for the convergent and discriminant validity of the RPI. The findings suggest that the RPI may be a useful tool that can be used to assist with the selection of patients for psychotherapy.