This chapter offers a comprehensive exploration of hearing impairment, a widespread condition characterised by a partial or complete loss of hearing that can affect individuals from birth or develop later in life. It examines the diverse types and degrees of hearing loss, the significant daily challenges faced by those affected, and the broad implications for communication, education, mental health, and social participation. Drawing on recent systematic reviews and meta-analyses, this chapter investigates key research questions around intervention effectiveness, diagnostic methods, risk factors, and the impact of hearing loss across the lifespan. It balances a strong methodological foundation with recognition of research gaps and emerging issues. Designed for a wide audience—including clinicians, researchers, policy-makers, educators, people with hearing impairments, and technology developers—it aims to support evidence-based practice, inform policy, and inspire future research. This chapter sequentially explores clinical and communicative outcomes, diagnostic challenges, psychosocial impacts, research opportunities, and presents insights to foster a multidisciplinary understanding of hearing impairment and its management.