This PhD thesis describes the search for, and analysis of, substructure in the phase-space distribution of stars within 1-2 kpc of the Sun. Such substructure, caused by stellar streams, is an important diagnostic of stellar dynamics and hierarchical formation of the Galaxy. While possibly phase-mixed, stellar streams remain detectable as coherent features in the space of integrals of motion. This thesis describes the development of new search techniques in phase- and Fe/H]-space to derive "effective" integrals of motion that are most suitable for a comparison with the observables. An...