The purpose of this work is to identify issues regarding the concept of validity in educational and psychological testing on which there is, and is not, consensus among experts, using an online Delphi study. Although many theorists have expressed their views about the proper characterization of validity, it is important to systematically collect ideas about each aspect of validity. Study participants were recognized academic experts who have led the discussion on the concept of validity in publications and academic meetings in Europe and the United States during recent decades. The Delphi study’s results identify some aspects of the concept of validity, the Standards (2014), and validation about which experts are at an impasse, and others about which consensus can be reached. Based on our findings, some recommendations to advance the conceptualization of validity are offered.