  Stellar-mass black holes (BHs), with masses comparable to stars, are a major
constituent of our Milky Way galaxy. This chapter describes the landscape of
challenging, and long-sought efforts to identify these objects in the Galaxy.
The first stellar-mass BHs were identified as persistent, but highly variable
cosmic X-ray sources. Later, transient BH candidates were detected, and now far
outnumber the persistent sources. Decades of effort have also yielded candidate
BHs via gravitational microlensing and their orbital effect on binary
companions. Populations of BH systems have begun to emerge from these detection
strategies, offering insight into the astrophysical context in which BHs exist
and driving questions about the formation, assembly, and ongoing evolution of
these enigmatic objects.
