Marginalized older adults represent a diverse spectrum of individuals coming from different social groups, including those who are racialized, those who identify as LGBTQ (lesbian, gay, bisexual, transgender, and/or queer), 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 status backgrounds. Marginalized geriatric patients are a heterogeneous group with unique physical and mental health issues that require recognition in order to optimize psychiatric assessment and treatment. Recognizing the impact of social determinants of health in geriatric patients who are marginalized is an important capacity for all healthcare practitioners to possess; recognizing the complexity that older marginalized patients bring to 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 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. Given that it would be impossible to include all potentially marginalized groups within this chapter, 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.