The SARS-CoV-2 Spike (S) glycoprotein is a trimeric class I fusion protein that mediates viral attachment, ACE2 receptor engagement, and membrane fusion. Each protomer consists of an S1 subunit containing the receptor-binding domain (RBD) and N-terminal domain (NTD), and an S2 subunit comprising the fusion peptide, heptad repeats, and transmembrane region. Proteolytic cleavage at the S1/S2 and S2 sites by host proteases such as furin or TMPRSS2 triggers the conformational rearrangements required for viral entry. As the principal surface antigen, Spike is highly immunogenic and the primary target of neutralizing antibodies and COVID-19 vaccines, with mutations in the RBD and NTD driving immune escape in emerging variants. Catalina’s SARS-CoV-2 Spike antibodies are stringently validated to deliver high specificity and reproducibility, supporting research in virology, variant characterization, vaccine development, and antibody therapeutics.