The technique of X-ray energy dispersive spectroscopy (XEDS) spectrum imaging in a dedicated scanning transmission electron microscope (STEM) is discussed in relation to its applicability to bimetallic nanoparticles. It is shown that the recent availability of aberration corrected microscopes and multivariate statistical analysis (MSA) techniques has allowed us to overcome many of the intrinsic limitations previously encountered when attempting STEM-XEDS spectrum imaging on nanoscopic volumes of material. We demonstrate through a variety of applications to Au-Ag and Au-Pd bimetallic nanoparticle systems, that STEM-XEDS can provide invaluable high spatial resolution compositional information on (i) alloy homogeneity and phase segregation effects within individual nanoparticles, (ii) particle size-alloy composition correlations, (iii) the detection of trace amounts of alloying element and (iv) metal component distribution in extremely highly dispersed catalyst systems.