I will describe some recent studies from my group on the theory and simulation of time-resolved spectroscopic measurements on the femtosecond timescale. We have recently rebuilt the basic descriptions of both ultrafast transient absorption spectroscopy (TA) and femtosecond stimulated Raman spectroscopy (FSRS, or fissors) directly in terms of the nuclear wave-packet dynamics underlying time-resolved signals. In both cases, the emphasis is on connecting the vibrational quantum-beat structure observed in spectroscopic signals with the signal-formation and molecular dynamical processes at work in these measurements. I'll additionally detail our recent work toward a mixed quantum-mechanical/semiclassical theory for the simulation and interpretation of four-wave-mixing and other measurements on small molecules embedded in low-temperature host crystals.