In the ETF world, assets under management is everything. For the issuers, it’s a matter of survival. An ETF that fails to attract investors will eventually be quietly put to rest or merged into another ETF from the same family. For investors, there is comfort in numbers. The ETFs listed below aren’t necessarily the biggest in each category, but they are showing rapid growth. When choosing how to implement your asset allocation strategy, pay attention to these fast growers because they are attracting the attention of the big money players like pension funds and college endowments.