Our research is aimed at time-resolved optical study and control of condensed matter structural changes and the collective modes of motion through which they occur. How do phase transitions or other collective structural rearrangements in crystalline solids occur, where huge numbers of molecules or ions move cooperatively into new positions? What are the dynamics, and how are they mediated by the lattice vibrational modes? Can we guide or control them with ultrashort optical pulse sequences? In crystalline chemical reactions, how do the neighbors surrounding the reacting species cooperatively accommodate fragments? What are the interactions between the reactive molecular modes and the lattice vibrations, and how do these influence reaction dynamics and outcomes? Can the complex structural relaxation dynamics of viscoelastic fluids and polymers, starting on subpicosecond time scales and sometimes extending for seconds, be understood in terms of a comprehensive statistical mechanical theory? Can we gain experimental access to the collective motions involved and measure them over all of the relevant time scales?