We investigate physical properties of complex systems characterized as complex fluids (a.k.a. "Soft Matter Physics"), which involve different examples, such as colloids, polymers, emulsions, gel, membranes, liquid crystals, as well as biological macromolecules. Complex fluids are widely found in our everyday life (e.g. in plastics, shampoo, soap, cosmetic products, yogurts, inks, etc.) and in biological systems, therefore, they not only attract interest due to their clear scientific value, but also for technological applications, besides stimulating the production chain of several economic segments. Characterization of complex fluids is a relatively new research field, which became more evident with the studies of Prof. Pierre de Gennes, which resulted in the Nobel Prize in 1991. It is important to point out the interdisciplinary aspect of these systems, connecting issues typically related to Physics with other areas of research, such as biology, chemistry, materials science, advanced computational techniques and mathematics. In particular, the formalism of Statistical Physics, thermodynamics, and fluid dynamics are of great importance in the theoretical description of these complex fluids. The Condensed Matter Theory group applies theoretical methods, based on advanced numerical/computational techniques along with analytical calculations, in order to provide theoretical insights about these systems.