BlackRock’s (NYSE: BLK) iShares unit, the world’s largest issuer of exchange traded funds, was the leading gather of ETF assets in the second quarter.

iShares pulled in $21.4 billion in new ETF assets during the April through June period, besting rival Vanguard by nearly 18%, reports Christopher Condon for Bloomberg.

iShares’ second-quarter leadership was buoyed by investors returning to emerging markets, which included nearly $6 billion of inflows to the iShares MSCI Emerging Markets ETF (NYSEArca: EEM). Including EEM, three iShares ETFs ranked among the top-10 ETFs overall for second-quarter inflows. The other two are the iShares Core S&P Mid-Cap ETF (NYSEArca: IJH) and the iShares 7-10 Year Treasury Bond ETF (NYSEArca: IEF).

Second-quarter inflows to EEM were more than quadruple the flows to the Vanguard FTSE Emerging Markets ETF (NYSEArca: VWO). [Emerging Markets ETFs Gaining Plenty of Cash]

Investors also continued allocating cash to emerging markets bonds ETFs last quarter with the iShares J.P. Morgan USD Emerging Markets Bond ETF (NYSEArca: EMB) pulling in over $1.2 billion. EMB’s primary rival, the PowerShares Emerging Markets Sovereign Debt Portfolio (NYSEArca: PCY), added $203 million while the Vanguard Emerging Markets Government Bond ETF (NasdaqGM: VWOB) brought in $23 million. [Risk-Taking Fuels Flows to EM Bond ETFs]

Underscoring the oft-overlooked point that plenty of other ETF issuers not named Vanguard are also gathering assets, State Street’s (NYSE: STT) State Street Global Advisors, the second-largest U.S ETF sponsor, added $8.3 billion last quarter, according to Bloomberg. [The Truth Behind the ETF Race]