One of the important challenges in current synthetic strategies is to design chain molecules, oligomeric or polymeric, which can reversibly self-organize into supramolecules structures with desired shape, size and functionality. These include short copolymers and small hydrogen bonding molecules of molecular weights less than 1kD, which can spontaneously assemble into well-defined nanostructures with molecular weights in the 102kD range. At the other extreme, associating polymers in solution reversibly assemble into infinite gels. These self assembled systems, which thus span the size range from nanoscopic to macroscopic, have applications in varied context, e.g., as viscosity modifiers for oils, in food (starches, gelatin), and in optoelectronic applications. The current understanding of the connection between the microscopic architecture of the building blocks and the resulting supramolecular structure is a nascent stage. As we shall show, the factor governing self assembly and the phase behavior of these materials are closely related. Therefore, we propose to utilize a suite of novel computer simulation methods, developed to simulate phase equilibria in complex fluids, to understand these interrelated issues. Specifically, we shall address the following problems as part of the proposed research: (a) The microphase separation and resulting self assembly of short copolymers into nanostructures, (b) The supramolecular assembly of macromolecules with associating moieties into thermoreversible gels and (c) The role of self assembly of polyampholyte solutions in determing their phase behavior. Through this approach we shall provide much deeper insights into this relatively new strategy of creating materials with highly defined structure and properties.