During its rather brief history, Nuclear Magnetic Resonance (NMR) spectroscopy was initially used by physicists. It was only in the 1960’s when the chemical shift was discovered that the chemical community started to use it and the field took off. NMR became an indispensable tool in structure elucidation of pure compounds and until late 1980’s this remained the most important type of application. Nowadays, the Nuclear Magnetic Resonance (NMR) Spectroscopy is the most powerful method for structure determination of organic compounds in solution state. If for crystalline compounds X-Ray crystallography is the ultimate structural proof, for a higher number of liquid compounds and amorphous solids, NMR is the best structural elucidation tool known to date. The success of the NMR method for structure elucidation of pure compounds makes this type of NMR application by far the most used one. Once the high field NMR spectrometers entered the chemical community, the method started to be used also for complex mixture analysis, penetrating new fields like medicine or food sciences. When it comes to applications of NMR to complex systems, like biological ones, one should carefully balance between the excitement of the “potential” of the technique and claims of “ultimate diagnosis tool capabilities”. Thus, one should be always aware which techniques and protocols are valuable but restricted to advanced medical research and which ones can be already extended to clinical practice. The present paper starts with examples of structure elucidation of isolated compounds, and moves to spectra of complex body fluids, discussing some experimental factors, reproducibility, and data interpretation via either biomarker identification approach or blind statistical classifier approach.