Galaxy clusters, as the largest peaks in the cosmic density field, play an important role in astrophysics and cosmology. As the most dramatic features of large-scale structure, the abundance of clusters provides a key opportunity to test our understanding of structure formation and cosmic expansion history. In recent years, observational astrophysics has been revolutionized by large surveys, yielding large optical cluster catalogs allowing for precision tracking of the growth of structure. The red galaxies that enable efficient detection and measurement of galaxy clusters can also be used to track growth of structure over a larger mass range. In this talk, I will discuss the redMaPPer cluster finder and associated redMaGiC catalog of red galaxies, and applications to cosmological measurements in the Dark Energy Survey (DES) and the Large Synoptic Survey Telescope (LSST), with particular focus on recent DES Year 1 cluster cosmology results and new challenges.