Background <p>Classical definitions of immunochemistry have traditionally emphasized antigen–antibody interactions and conventional immunoassays. However, rapid advances in molecular engineering, nanotechnology, computational modelling, and systems immunology now extend the field far beyond its historical scope.</p> Objective <p>This study aims to critically examine existing definitions of immunochemistry and develop a concise, contemporary definition that reflects current scientific and technological advancements.</p> Methods <p>A qualitative conceptual approach was employed, integrating a systematic literature review (1950–2024), 12 semi-structured expert interviews, and a two-round Delphi consensus process. Data were analysed using thematic coding with triangulation across literature, expert insights, and Delphi outcomes to ensure methodological rigour and conceptual validity.</p> Results <p>Three major themes emerged: (1) prevailing definitions remain narrow and remain limited in scope; (2) experts strongly support the need for redefinition; and (3) four core conceptual domains characterise modern immunochemistry: chemical interactions, molecular design, functional applications, and interdisciplinary convergence. Consensus was achieved at ≥ 75% agreement with stable ratings across Delphi rounds.</p> Conclusion <p>Immunochemistry has evolved into an interdisciplinary science integrating analytical chemistry, molecular biology, synthetic biology, systems immunology, and computational approaches. The proposed contemporary definition better captures this expanded scope and offers clearer guidance for education, research, laboratory practice, and emerging biomedical technologies.</p>