To understand the functional integrity of the whole living organism, it is important to have a clear understanding of the interactions between individual cells and a single molecule within these cells. With the latest biomolecular/cellular imaging technology, researchers are focusing on investigating such biological interactions at both molecular and cellular levels. This involves direct imaging of the “presence” of single molecules and individual cells as well as the use of real-time imaging of dynamic, reversible biological signaling “events” such as protein-protein interaction, protein modification andintracellular calcium changes. Moreover, this imaging technology can be combined with the protein manipulation techniques to elucidate the functional contribution of these dynamic interactions and signal transduction events in the whole living organism.