The demand for critical care is on the rise and is expected to grow significantly in coming decades. Health-related quality of life (HRQoL) is a relevant outcome measure for patients recovering from critical illness. This chapter addresses several key questions about HRQoL, namely: Why measure HRQoL in critically ill patients? What do we mean with HRQoL? Which HRQoL instruments are being used? How to estimate HRQoL before ICU admission, and what is the impact of critical illness on HRQoL, particularly in the elderly? This chapter also addresses the phenomenon of response shift in survivors of critical illness related to their perceived HRQoL. It is argued that HRQoL measures for physical and psychological factors, functional status, and social interactions should be incorporated as standard quality indicators of ICU performance. These measurements will provide further insight on long-term post-ICU recovery and might be used to evaluate and track the utility of follow-up clinics after hospital discharge.