The Standard Penetration Test (SPT) and Cone Penetrometer Test (CPT) have become industry standards for subsurface geotechnical investigations using small diameter (< 8-in. [20-cm]) borings and soundings. Both procedures have evolved over a period of 100 and 70 years, respectively, and have been adopted as ASTM standards. Each procedure has certain advantages over the other, but both can elicit incorrect data under particular subsurface conditions that are often overlooked, depending on the experience of field personnel operating or logging the tests. This paper seeks to explain the operative assumptions employed in both procedures, highlight the various corrections that are commonly employed, and warn the reader of common errors in interpretation. The article concludes by stating that, under most conditions, the joint employment of SPT and CPT together has the greatest potential for characterizing sites correctly.