The behavioral and psychological symptoms of dementia (BPSD) are a heterogeneous set of challenging disturbances of behavior, mood, perception, and thought that occur in almost all patients with dementia. A huge number of instruments have been developed to assess BPSD in different populations and settings. Although some of these tools are more widely used than others, no single instrument can be considered completely satisfactory, and each of these tools has its advantages and disadvantages. In this narrative review, we have provided a comprehensive overview of the characteristics of a large number of such instruments, addressing their applicability, strengths, and limitations. These depend on the setting, the expertise required, and the people involved, and all these factors need to be taken into account when choosing the most suitable scale or tool. We have also briefly discussed the use of objective biomarkers of BPSD. Finally, we have attempted to provide indications for future research in the field and suggest the ideal characteristics of a possible new tool, which should be short, easy to understand and use, and treatment oriented, providing clinicians with data such as frequency, severity, and triggers of behaviors and enabling them to find appropriate strategies to effectively tackle BPSD.