The lack of demographic data on sexual orientation and gender identity (SOGI) in the United States has long perpetuated the invisibility of LGBTQ+ populations in research, policy, and service provision. This exclusion is rooted in structural oppression, including discrimination, stigma, and legal inequality, which shape societal attitudes and dictate whose lives are deemed worthy of focus and study. As a result, researchers, policymakers, service providers, and advocates face significant challenges in addressing the unique needs of LGBTQ+ communities, from understanding population size and demographic characteristics to quantifying and intervening in disparities across areas such as health, economic security, and civic representation. As an increasing proportion of the U.S. population publicly identifies as LGBTQ+—in 2024, the best available data indicated that 7.6% of all U.S. adults identified as LGBTQ+, with significantly larger proportions among younger generations—the need for accurate and consistent SOGI data is more pressing than ever. This chapter examines critical considerations for measuring SOGI, including the multidimensional nature of these variables, evidence-based best practices, and the contexts in which data are collected, such as surveys, administrative systems, and service settings. Key issues such as privacy, confidentiality, misuse, and the need for proper training in SOGI data collection are also addressed. The chapter then explores advancements in SOGI measurement and policy at the state and federal levels, concluding with a discussion of future directions for inclusive and equitable SOGI data collection. By advancing rigorous and ethical approaches to collecting and utilizing SOGI data, researchers, policymakers, and advocates can better understand and address the needs of LGBTQ+ communities, ultimately promoting equity and accountability in policy and practice.