Simple Summary: Understanding the psychological correlates of attitudes toward pet relinquishment and actual pet relinquishment is essential to inform interventions, and assess their impact. In this study, we developed new scales to measure attitudes toward pet relinquishment, motives for pet relinquishment, and general trust in pets. With these scales, we showed that attitudes of lack of obligation toward pet relinquishment were more likely in older people, those who perceived their pet as a burden, and those with lower general trust in pets. In addition, we found that attitudes of pragmatism toward pet relinquishment were more likely in men, those who were the main pet caretaker, those who perceived their pet as a burden, those with higher motives for pet relinquishment, and those with lower general trust in pets. Moreover, we found that past pet relinquishment behavior was more likely among people with attitudes of pragmatism toward pet relinquishment. Broadly, these findings advance our knowledge of pet relinquishment, and are likely to inform intervention campaigns to prevent it.Abstract: Understanding pet relinquishment is essential to inform interventions and assess their impact. In a cross-sectional study, we explored how attitudes of lack of obligation and pragmatism toward pet relinquishment correlated with, and differed according to, sociodemographic characteristics (age, gender, education, political orientation, religion, income, and household), previous animal experience, and owner perceptions of animals (perceiving pet as a burden, motives for pet relinquishment, regret having a pet, and general trust in pets). We adapted and developed three scales to measure attitudes toward pet relinquishment (ATPR), motives for pet relinquishment (MPR), and general trust in pets (GTP), revealing good psychometric qualities. Hierarchical linear regressions showed that attitudes of lack of obligation toward pet relinquishment were stronger in older people, those perceiving their pet as a burden, and those with lower general trust in pets. Attitudes of pragmatism toward pet relinquishment were stronger in men, those who were main pet caretakers, those perceiving their pet as a burden, those with higher motives for pet relinquishment, and those with lower general trust in pets. Furthermore, results showed that past pet relinquishment behavior was predicted by attitudes of pragmatism, but not attitudes of lack of obligation.