Underserved communities face persistent systemic barriers that create and perpetuate disparities across multiple domains of social life, including healthcare access, energy equity, social care, disaster preparedness, and economic inclusion. Despite growing scholarly attention to these populations, significant gaps remain in understanding how overlapping forms of disadvantage interact and how research methodologies can be ethically and effectively adapted to generate actionable knowledge. This paper presents a comprehensive conceptual framework for understanding underserved communities through the integration of community engagement theory, methodological innovation for data-obscured populations, and intersectional analysis of structural barriers. Drawing on a systematic synthesis of the social science literature, the paper identifies four core dimensions that shape the experiences of underserved communities: (1) structural and institutional barriers, (2) trust and relationship dynamics, (3) methodological challenges in research and practice, and (4) community assets and resilience. This paper proposes an integrated framework, the Community Equity Engagement and Research (CEER) model, that emphasizes partnership, cultural responsiveness, and methodological flexibility. The paper concludes with implications for policy, practice, and future research, arguing that meaningful progress requires shifting from deficit-based approaches to strengths-based, participatory frameworks that center community voice and agency.