Janet B. W. Williams (born November 15, 1947) is an American social worker who focuses on the diagnosis and assessment of mental disorders.

She was a major force in writing the PHQ-9, a 9-question instrument given to patients in a primary care setting to screen for the presence and severity of depression.

[5] Williams has been recognized as an ISI Highly Cited Researcher, authoring over 230 scholarly publications throughout her career.

In 1974, the American Psychiatric Association started work on the third edition of its Diagnostic and Statistical Manual of Mental Disorders (DSM-III), and appointed Robert Spitzer (Williams’ husband) to lead the effort.

In the mid-1990s, Williams (along with Robert Spitzer and Kurt Kroenke) developed the PHQ (Patient Health Questionnaire) and the PRIME MD (Primary care Evaluation of Medical Disorders), both of which were designed to help primary care physicians screen for the presence of mental disorders and the severity of depression.