Extreme temperatures impact human health and well-being. Yet, very little empirical evidence exists on what determines human resilience, both in general and in relation to specified extreme temperatures. This paper addresses this serious gap in knowledge by developing a quantitative measure of general resilience (i.e., the resilience of individuals to all daily life circumstances). This is complemented with qualitative elicitations of specified resilience (i.e., the resilience of individuals to a particular type of threat, stress, or event), which in this study are extreme heat and extreme cold. This research uses the “sense of coherence” (SOC) approach (i.e., Orientation to Life Questionnaire—SOC-13 scale) to develop a general resilience index (GRI) using a composite index approach and to develop assessments of heat-related resilience (HRR) and cold-related resilience (CRR) using primary data from mixed-method interviews with 52 older people living in Lisbon, Portugal. The findings show that most participants exhibited high levels of general resilience but low levels of specified resilience. In particular, resilience to cold was lower than resilience to heat. Sources of general and specified resilience were found to be dependent on cognitive, behavioral, and motivational factors in older people’s lives. The findings reveal that believing threats (e.g., extreme temperatures) are structured and ordered, perceiving that assets are available to respond to them, and feeling it is worth responding are sources of resilience. Concrete policy recommendations can be generated from this study by both central and local governments to strengthen resilience. These can take the form of programs, plans, and actions that support individuals and enable them to better deal with challenging life events such as extreme temperatures and to improve both general and specified resilience.