Reliable, valid, and efficient assessment of depression is critical to identify individuals in need of treatment and to gauge treatment response. Current methods of assessment are limited to subjective measures of patient self-report and clinical interview. They fail to take into account observable measures of behavior that could better inform detection of the occurrence and severity of depression. Recent advances in computer vision, signal processing, and machine learning have potential to meet the need for improved depression screening, diagnosis, and ascertainment of severity (i.e., assessment). This chapter reviews these advances. We describe multimodal measures of behavior and physiology, how these measures can be processed to extract features sensitive to depression, and how classification or prediction may be used to provide automatic assessment of depression occurrence and severity. Following an overview in Sections 2 of how behavioral and physiological sensor signals can be processed in a multimodal manner, Sections 3 to 6 discuss in detail how to extract features sensitive to depression, based on insights from earlier scientific investigations and from studies of existing clinical assessment. These latter Sections also touch on key machine learning methods that have been adopted to date. Of particular interest is the fusion of information from different modalities, and Section 7 discusses fusion in the context of both classification and prediction. For researchers investigating automatic analysis of depression, high quality research data is a critical concern. Similarly important for the practical application of multimodal depression assessment systems is their likely context of use. Both concerns are discussed in Section 8, while Section 9 provides an overview of key challenges in this research area. In this chapter, the focus is primarily on depression. This emphasis reflects the emphasis in the field. Most work to date on automated, multimodal assessment of psychopathology has focused on depression. Other disorders, such as post-traumatic stress disorder, generalized anxiety disorder, traumatic brain injury, suicidality, dementia, Alzheimer's disease, schizophrenia, Parkinson's disease, and autism spectrum disorder have received less attention and accordingly are not discussed in detail. The approaches and many of the methods we discuss, nevertheless, are applicable to disorders that share behavioral features, are comorbid with depression, or otherwise share variance with depression. Dimensional models of psychopathology [HiTOP, Undated; Kotov, Gamez, Schmidt, & Watson, 2010] in particular group unipolar depression (Major Depressive Disorder and Dysthymia), Generalized Anxiety Disorder, PTSD, and in some models Borderline Personality Disorder together as distress orders. From this perspective, the research we review on depression is relevant to these disorders as well. 1. Depression Depression is one of the most common mental disorders [Kessler, Chiu, Demler, and Walters, 2005] and a leading cause of...