I find the intellectual questions thrown up by benchmark indices absolutely fascinating. Talk to the providers about what it is they do exactly and most of them will say they hold a mirror up to the investable world as it exists, while simultaneously acknowledging that their decisions can end up reshaping just what that reflection looks like. What everyone can agree on: their role in a market increasingly dominated by passive investing is growing.

So here are 2,000 words or so on the index providers who rule the world … as well as the people who want to unseat them.

Benchmark indexes trace their history to the late 1800s, when Charles Dow, co-founder of Dow Jones & Co., created the first as a way to gauge the general direction of the market (and to sell newspapers). Today the number of benchmarks outnumbers that of individual stocks. “The problem is that a lot of investors assume that the benchmarks are almost God-given and that they’re ­problem-free. Most of the time they’re not,” says Mohamed ­El-Erian, chief economic adviser at Allianz SE and a Bloomberg View contributor. “It’s a crucial issue. And it’s becoming even more important as more and more people migrate to passive products.”

Index Providers Rule the World—For Now, at Least – Bloomberg Markets Magazine