Spanish Validation and Psychometric Properties of the FIAT-Q-Brief Scale for Functional Idiographic Assessment. Contextual therapies address psychological problems and human suffering through verbal changes and natural contingencies given in therapy. Among them, Functional Analytic Psychotherapy (FAP) has developed a clinical process focused on the functional analysis of clinically relevant behaviors, which have to appear and be modified directly by the therapist within the consultation. The Functional Idiographic Assessment Template-Questionnaire is used to assess these functional classes. Here we present the Spanish adaptation and scoring of an abbreviated format in the FIAT-Q-breve. The sample consisted of 400 participants (52.3% female and 47.8% male), with a mean age of 36.21 (SD= 14.24), and a small sample of 27 participants was also used for test-retest reliability. The FIAT-Q-breve questionnaire itself, together with other life problems and life values questionnaires (SA-45, VLQ and LSI) have been applied on-line. Results show a very high overall factor reliability (α= 0.95, ω= 0.96); factor reliability α between .63 and .90; and test-retest reliability r between .65 and .80. The FIAT-Q-breve correlates with the SA-45, both about psychopathological problems, and does not correlate with the values questionnaires (VLQ and LSI). All five factors of the original questionnaire appear in the CFA, although the model does not fully fit. We provide the data for the assessment of other consultants and discuss the usefulness and use of the FIAT-Q-breve for assessment in contextual therapies