2025 / Loneliness is more prevalent in people with schizophrenia spectrum disorders (SSD), compared to the general population. Loneliness is a consequence of perceived low quality of social interactions (Hawkley et al., 2003), thought to be influenced by social cognitive biases Characteristic symptoms, including paranoia, social anxiety, and depression, leaving those with SSDs especially vulnerable to loneliness. Nonetheless, the mechanisms of loneliness have not been directly examined among people with SSDs. Thus, the goals of this dissertation were to examine the extent to which negative social cognitive biases contribute to loneliness among people with SSDs. In Study 1, I used a Loving and Kindness Meditation (LKM) exercise (Fredrickson et al., 2008) to determine whether reducing negative social biases could decrease feelings of loneliness. In Study 2, I examined associations between social cognitive biases and loneliness in daily life using ecological momentary assessment (EMA). Results indicated that LKM did not reduce loneliness, or negative social biases; however, negative social biases did reduce across both groups, with the control group showing a greater reduction than LKM. Results from study 2 showed that participants varied in their loneliness and negative social beliefs across time, and loneliness and negative social beliefs were strongly related to negative affect in the context of daily life. Study 2 also showed that internalized stigma, depression, social anxiety, and paranoid ideations are related to momentary loneliness suggesting that enduring characteristics associated with negative beliefs exacerbates momentary loneliness. This study underscores the role of both cognitive and emotional factors in driving loneliness. The significant correlations between EMA and trait measures suggest that even in the absence of high loneliness, there is consistency in how these patterns manifest across time in daily life. Together, these studies shed light on the mechanisms contributing to loneliness in SSDs, as well as the predictors and consequences of loneliness in daily life.