Advances in immunotherapies across cancer, vaccines, autoimmunity, and biologics have highlighted the critical need for comprehensive metrics that capture immune dynamics beyond traditional reductionist measures such as antibody levels, lymphocyte counts or cytokine profiles. The concept of an ImmunoScore, a quantitative, algorithmic measure of immune activity, can address the gap by integrating multidimensional data on immune cell composition, localization, activation states, and structural context. Originally developed in oncology to stratify prognosis based on CD3⁺ and CD8⁺ T-cell density and spatial distribution within tumors, ImmunoScore has demonstrated superior predictive value compared to conventional staging systems. With the advent of high-dimensional platforms including single-cell sequencing, spatial transcriptomics, imaging mass cytometry, and systems serology, the ImmunoScore framework has expanded to encompass vaccine-induced signatures, tumor microenvironment profiling, autoimmune disease markers, and in silico modeling of immune responses. This review synthesizes the advances and clinical applications of ImmunoScore across four domains: i) systems immunology in vaccinology, ii) cancer immuno profiling and therapy prediction, iii) autoimmune disease-activity markers, and iv) computational approaches for predicting immune response to biologic therapeutics. We propose that a standardized ImmunoScore can serve as a unifying metric to assess immune competence, guide therapeutic decisions, predict adverse events, and enable precision medicine across diverse clinical settings.