In this report the members of the Scientific Committee on Ocean Research Working Group 51 have attempted to describe the total process involved in obtaining salinity and temperature profiles with modern conductivity-temperature-depth (CTD) instruments. Their objective has been to provide a guide to procedures which will, if allowed, lead to the acquisition of good and consistent data sets. Successive chapters proceed from a discussion of the sensors through their calibration and operation, to a detailed discussion of data processing options. The final chapter gives guidelines for data exchange. Five appendices go into more detail on topics which include the design of an observational program; efficient low-pass filters; data exchange formats; the algorithm for Practical Salinity as a function of conductivity ration; and the determination of the ice-point correction of thermometers. (Author/ML)