  We provide a critical overview of the theory of the chirality-induced spin
selectivity (CISS) effect, i.e., phenomena in which the chirality of molecular
species imparts significant spin selectivity to various electron processes.
Based on discussions in a recently held workshop, and further work published
since, we review the status of CISS effects - in electron transmission,
electron transport, and chemical reactions. For each, we provide a detailed
discussion of the state-of-the-art in theoretical understanding and identify
remaining challenges and research opportunities.
