Over the last decade or so, there has been increasing attention paid to the concepts of equity, diversity, and inclusion (EDI) across the healthcare sector. Ensuring every patient has access to and receives appropriate, high-quality healthcare regardless of their identity[ies] is the goal of EDI-related initiatives in healthcare. Traditionally marginalized older adults represent a diverse spectrum of individuals, from different social groups, including those who are racialized, those who identify as LGBTQ+ (lesbian, gay, bisexual, transgender, and/or queer and other minority sexual orientations and gender identities), those who have a physical and/or developmental disability, those who are immigrants or refugees, those who are homeless, and/or those who come from low socioeconomic backgrounds. Marginalized older adult patients are a heterogeneous group with unique physical and mental health issues that require recognition and discernment in order to optimize psychiatric assessment and treatment. Recognizing the impact of the social determinants of health on older adult patients who are marginalized is an important capacity for all healthcare practitioners to possess; recognizing the complexity that older marginalized patients bring to the context of assessment and treatment is fundamental to providing appropriate, patient-centered, and anti-oppressive care to these individuals. A comprehensive assessment is an important step in the process of mitigating the unwanted negative effects of healthcare disparities for traditionally underserved populations. This chapter will focus on the concept of anti-oppressive practice as well as the importance of addressing the issue of culture as part of psychiatric assessment and treatment in older adults. It would be impossible to include all potentially marginalized groups within this chapter; therefore, we will focus on several traditionally underserved groups, including LGBTQ+-identified people, people who are racialized, people who are homeless, and people who have an intellectual or developmental disability.