To reverse the trend of declining wildlife populations globally, individuals must be provided with conditions that allow them to thrive, not just survive. It is no longer only the remit of conservation breeding programs to ensure animal well-being to promote reproduction; in situ conservation efforts must also consider how environmental and anthropogenic pressures impact wild populations and how to mitigate them, especially with regard to reproduction and survival. Stress and welfareWelfare are complex concepts that necessitate an understanding of how stressors affect animals on both individual and population levels, and how the subsequent impact on reproduction can vary. There are species differences in how factors impact well-being, related in part to natural history, which are also shaped by individual perceptions and coping abilities. A multitude of stress-related responses then have the potential to disrupt reproduction on many levels and, ultimately, fitness. A major limitation to advancing welfare science is the lack of definitive tests to verify welfare status, that is, is the animal thriving, or just surviving? While analyses of circulating or excreted glucocorticoids (GCs) have for decades been the primary method of assessing stress, today we recognize the need for more comprehensive indicators that reflect multiple physiological systems, including behavior, to assess both negative and positive welfare states. In this chapter, we discuss the potential for stress not only to disrupt but also sometimes to facilitate reproduction, including the key role that GCs play. We then discuss several other physiological biomarkers that have the potential to assess well-being in the context of reproduction and conclude with multi-biomarker approaches, which, if applied to wildlife, could be powerful tools for conservation and could help to elucidate the complex relationship between stress and reproduction.