Large biological molecules like proteins and RNA, carry out their functions by folding to well-defined three-dimensional structures. We are interested in the physical interactions that direct this self-assembly process. By combining microfabricated flow cells with synchrotron x-ray scattering, we have gained insight into the earliest steps of protein and RNA folding. A recent series of experiments indicates that the critical, first stage of RNA folding is dominated by electrostatic interactions.