A knowledge of the three-dimensional structure of a protein is essenti
al to understand how a protein performs its functions. It is also a pr
ime requirement for the rational design of novel sequences with specif
ic structural, chemical or catalytic properties. Until recently, such
information could only be obtained from X-ray diffraction studies on p
rotein crystals. In the past few years, however, nuclear magnetic reso
nance (NMR) spectroscopy in solution has rapidly become established as
an effective alternative method. This review briefly examines the two
techniques and their relevance to protein engineering and design.