Depression is one of the most ubiquitous and debilitating forms of psychological distress. About one in three youth experiences heightened depressive symptoms and one in five meets criteria for at least one episode of major depression before they enter adulthood. Early diagnosis is critical to ensuring youth receive the support they need, and yet often the symptoms associated with depression make conducting such an assessment challenging. In this chapter we review the many signs of depression, exploring the myriad of ways children experience and express signs of depression across stages of development, cultures, and contexts. To prepare for a comprehensive assessment, we outline the many factors that contribute to depression, ranging from the biological, intrapsychic, and cognitive, to the behavioral, interpersonal, and socioecological. We then describe the multimodal assessment techniques that must be implemented flexibly to identify symptoms and understand the contributing factors that underlie depression. Through case examples, we illustrate how assessment can be adapted for clients across ages and cultures and in varying assessment contexts. Finally, we describe the many options for addressing factors that contribute to depression.