Coherent optical control in both spatial and temporal dimensions is demonstrated. Lattice waves are generated by femtosecond pulses at one region of a crystal, monitored through spatiotemporal imaging which captures their propagation at lightlike speeds, and manipulated by additional pulses at other regions of the crystal distinct from the first. The capabilities demonstrated here enable terahertz polaritonics through enhanced optical control over propagating lattice excitations and ultrahigh-bandwidth, terahertz-frequency signals. (C) 2001 American Institute of Physics.