We review findings on spousal interrelations in old age in such key domains as cognition, well-being, and health. Therein, we demonstrate that spousal interrelations may extend developmental options but may also make an individual vulnerable to the experience of loss. We address theoretical questions concerning possible underlying mechanisms, e.g. individual and spousal goal-related processes. Furthermore, we draw attention to important methodological challenges such as identifying processes that operate along different time scales and employing adequate data analytic tools. We propose that aging research may benefit from an examination of interrelations in developmental pathways of multiple co-developing individuals such as spouses and point to the need to disentangle individual from relationship-specific effects.