NMR spectroscopy and molecular dynamics (MD) simulations are powerful approaches for probing aspects of conformational dynamics in biological macromolecules. Methods that can be utilized to characterize dynamics on picosecond-nanosecond and on microsecond-millisecond time scales will be illustrated by applications to the DNA-repair enzyme AlkB [Ergel, et al., 2014], the enzyme ribonuclease H [Stafford, et al., 2015], and the yeast transcription factor GCN4 [Gill and Palmer, 2015]. In the first example, NMR spin-relaxation measurements establish that the equilibrium distribution of ordered and disordered conformations of the nucleotide recognition element controls order of addition of substrates. In the second example, spin-relaxation measurements and MD simulations as a function of temperature for proteins from psychrotrophic, mesophilic, and thermophilic bacterial species characterize the coupling between conformational dynamics, stability, and function. In the third example, spin-relaxation measurements at five static magnetic fields and MD simulations lead to a two-step selected- and induced-fit mechanism of binding to DNA. Taken together, these cases illustrate the importance of rare, sparsely populated, conformational states in protein function.