Analytical methods for probing plant metabolism are taking on new significance in the era of functional genomics, metabolomics, and systems biology. Nuclear magnetic resonance (NMR) is becoming a key technology in plant metabolomics. Stable isotope labeling of cultured cells and higher organisms has been especially promising in that it allows the use of advanced heteronuclear NMR methodologies through a combination of in vivo and in vitro measurements. This new approach provides much better resolution of the metabolite mixture signals in the multidimensional NMR spectra than does the conventional one-dimensional 1H-NMR previously used in plant metabolomics. In this chapter, we describe the practical aspects of two key NMR technologies: uniform stable labeling of plants and in vitro heteronuclear NMR.