Replication of the viral RNA genome performed by the viral replicase is the central process during the viral infection cycle (Nagy and Pogany, see earlier chapter four). Most RNA viruses assign one or more proteins translated from their own genomes for assembling the viral replicase complex, which consists of the viral RNA, viral proteins, and several subverted host proteins embedded in cellular membranes. Understanding the various biochemical activities of the replication proteins can lead to target identification for human intervention to control viral infections or the damage to the host cells. The replicase proteins of tomato bushy stunt virus (TBSV) are selected as model system to study the dynamics of interactions between viral replicase proteins using surface plasmon resonance (SPR) analysis. The SPR assay provides real-time protein interaction data by measuring the change in refractive index at the surface of the sensor chip due to the change in mass resulting from the interaction between the immobilized protein and the protein that is being passed over the immobilized chip surface. SPR-based biosensor BIAcore X was used to carry out TBSV replicase protein interaction studies.