The high-order harmonic process is the first and best example of a complex process where attosecond time-scale dynamics can be coherently manipulated, thus representing the fastest technology yet devised by man. Useful examples of this manipulation include methods for phase matching the high-order harmonic process, for manipulating the spectral characteristics of the radiation, and for generating attosecond pulses. In this talk, I will discuss a variety of results from our group, including recent work that uses counter-propagating pulsetrains to manipulate the phase of the recolliding electron and thus increase the efficiency of the generation process. I will also discuss the unique characteristics of HHG that present both challenges and opportunities in exploiting it as a nonlinear-optical process.