The Positive and Negative Affect Schedule (PANAS) is a widely used measure for assessing levels of positive and negative affect. Its excellent psychometric properties make it a popular tool among researchers. This chapter provides an overview of the PANAS, outlining its theoretical background and describing its initial development and validation. It presents the results of factor analysis and reliability statistics, as well as evidence for its construct validity. It is important to note that affective measures such as the PANAS are particularly valuable in mindfulness research. The ability to regulate one’s affective states is a crucial component of mindfulness, and the PANAS can help researchers assess how mindfulness interventions impact affective states. This chapter also highlights more recent studies that support the psychometric properties of the PANAS and its usefulness in mindfulness research. The PANAS has been used in many languages and has demonstrated adequate reliability and validity across different cultures. Overall, the PANAS is an important tool for assessing affective states in research, particularly in the context of mindfulness interventions.