ABSTRACT. The Simanjiro plains, east of Tarangire National Park in Northern Tanzania are a key dispersal area for wildlife, and are of vital importance to Maasai pastoral livelihoods, which are rapidly diversifying. Diversification is coupled with fragmentation of the rangelands as agriculture expands and multiple actors compete for land. These changes reflect transformations occurring across pastoral rangelands, and pose the broader challenge of reconciling conservation and development objectives. We propose that qualitative research using a three-dimensional human well-being framework, encompassing material, relational, and subjective aspects, can inform locally legitimate and socially just conservation. Through semistructured group interviews across four villages, we explore well-being conceptions of Maasai men and women in Simanjiro. In particular we focus on the value of understanding social complexity for conservation research in the form of (i) the heterogeneity of conceptions of well-being across gender, age groups, and villages; (ii) temporal dynamics in notions and experiences. Material assets, namely land (for grazing and agriculture) and livestock are important to people but are intertwined with other aspects of well-being. Subjective well-being is centered on concerns about future security, especially with regards to land. Autonomy and social unity (relational dimension) are key priorities. We reflect on the implications for conservation at the study site, and more broadly on how well-being can better be incorporated into policy and practice that takes social justice seriously. The diversity we find in well-being priorities and experiences shows the importance of taking a disaggregated approach that conceptualizes benefits and burdens across a range of locally important well-being components ensuring the priorities of the most marginalized groups are represented.