This chapter discusses the practice of measurement in psychological research. Here, where we cast doubt on the basic assumptions and endeavours underlying the act of measuring in mainstream psychology. Next, we introduce the processual alternative, which stresses the study of activity as situated and coupled with an environment. This chapter explains how a process approach to ‘measurement’ is thus fundamentally different from the standard one, and can remedy existing issues related to non-ergodicity and the ecological fallacy. These ideas are illustrated by means of the concept of intelligence, which is undoubtedly one of psychology’s show-pieces of measurement.