Indexing refers to the norms used by news organizations to select news sources and frames. When indexing norms become widely shared across organizations, media systems may display familiar national characteristics and act as an institution. The most common indexing norm found in many democratic press systems is to index sources and their views according to the power balances that journalists perceive to exist among actors in political institutions involved with particular political conflicts or policy processes. New areas of research include how changes in media systems, such as fragmenting audiences and proliferating media channels, may change source selection, framing, and weighting routines. In particular, the growth of right‐wing media networks that interact with elected politicians has weakened the capacity of legacy news organizations to act as gatekeepers that index the sources and framing of public debates.