In the evolving landscape of transplant medicine, the shift from traditional antigen-level matching to molecular matching represents a definitive leap forward in our ability to predict and prevent alloimmune responses. This booklet is dedicated to the science and application of two complementary computational technologies delivered by the TxPredictor: PIRCHE and Snow molecular matching. Together, these tools redefine how we view immunological compatibility by addressing both arms of the adaptive immune response. Invented by Eric Spierings at the University Medical Center Utrecht in the Netherlands, the PIRCHE algorithm is designed to quantify the risk of indirect alloresponse in transplantation. PIRCHE predicts the specific mismatched peptides likely to be presented by HLA to T-cells (i.e. T-cell epitopes). The later developed PIRCHE Snow algorithm focuses on antibody recognition, utilizing advanced structural modeling to predict which mismatched amino acids on the donor HLA surface are accessible to antibodies (i.e. B-cell epitopes). By combining the T-cell perspective of PIRCHE with the antibody-accessibility insights of Snow, TxPredictor enables a "dual-pathway" view of immunological risk that classic antigen matching misses. Within The Handbook, you will find a comprehensive overview of the biological mechanisms driving allorecognition, a summary of the robust clinical evidence linking these scores - both individually and in conjunction - to dnDSA formation, rejection and graft survival, as well as a practical user guide for integrating TxPredictor into your workflow. Our goal is to empower you with the tools to move towards truly personalized, comprehensive risk stratification for improved patient management.