  Magnetic activity is a ubiquitous feature of stars with convective outer
layers, with implications from stellar evolution to planetary atmospheres.
Investigating the mechanisms responsible for the observed stellar activity
signals from days to billions of years is important in deepening our
understanding of the spatial configurations and temporal patterns of stellar
dynamos, including that of the Sun. In this paper, we focus on three problems
and their possible solutions. We start with direct field measurements and show
how they probe the dependence of magnetic flux and its density on stellar
properties and activity indicators. Next, we review the current
state-of-the-art in physics-based models of photospheric activity patterns and
their variation from rotational to activity-cycle timescales. We then outline
the current state of understanding in the long-term evolution of stellar
dynamos, first by using chromospheric and coronal activity diagnostics, then
with model-based implications on magnetic braking, which is the key mechanism
by which stars spin down and become inactive as they age. We conclude by
discussing possible directions to improve the modeling and analysis of stellar
magnetic fields.
