Revision with unchanged content. Chemical shifts provide detailed information about non-covalent structure, solvent interactions, ionization constants, ring orientations, hydrogen bond interactions, and other phenomena. Since different chemical shift data sets are not necessarily comparable without corrections or adjustments, the applicability of statistical analysis of NMR chemical shifts to biomolecules has so far been limited. We use the term "congruent" to describe data sets that can be directly used for statistical analysis after proper adjustments. Congruence problems in chemical shift analysis can occur at three different levels. (1) At the protein level, when using collections of chemical shifts of proteins reported by different groups. (2) At the residue level, when using collections of chemical shifts of different residues, here random coil chemical shifts must be subtracted. (3) At the refined residue level, when using collections of chemical shifts of same residues, neighboring residue effects on the chemical shifts need to be taken into account. In this book, these correction or adjustment problems are addressed based on the newly proposed robust statistical models.