Every interviewee will respond differently to the interview process and may be prone to factors known to negatively impact on information-gathering. There are many factors that will impede this process. These factors may also influence the quality, quantity and accuracy of information provided by an interviewee. Most of these factors are related to memory processing and vulnerabilities. Broadly they include memory, emotions, trauma/stress and cognitive ability or vulnerabilities. This chapter will explore these factors and discuss how they impact on the interviewing process. The purpose of this chapter is to provide an overview of the psychological concepts that impact on investigative interviewing and provide guidance on best practice methods to recognise and manage the challenges associated with them.