It is important to elucidate molecular structures of polymer and biological molecules at interfaces because such structures mediate functions of these molecules. However, it is difficult to examine such interfaces in situ in real time due to the lack of appropriate tools. In the recently years, we have used a nonlinear optical laser spectroscopy, sum frequency generation (SFG) vibrational spectroscopy, to investigate molecular structures of interfacial polymer and biological molecules in situ.