The selection and the use of a measurement instrument is an extensive and complex process forming the backbone of any actions in health psychology research. This chapter discusses five steps which may guide this process. In the first step, researchers and practitioners consider broader purpose and/or choose domains of measurement. The following steps refer to considering the specificity and characteristics of the target population (e.g., age, culture) (Step 2) and the optimal type of measurement (e.g., self-report vs. biomarker) (Step 3). The process is completed with deliberations referring to psychometric characteristics (Step 4) and aspects of implementation (Step 5) of an instrument.