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]

Fidelity, which entered the ETF arena in earnest last October with the introduction of 10 sector ETFs, now has over $1 billion in ETF assets under management and at least four of its sector funds have over $100 million in AUM.

Illinois-based First Trust, the issuer of well-known ETF such as the First Trust Dow Jones Internet Index Fund (NYSEArca: FDN) and the First Trust NYSE Arca Biotechnology Index Fund (NYSEArca: FBT) had $23.9 billion in ETF assets at the end of the first quarter and $27.7 billion as of June 30, making it the sixth-largest U.S. ETF issuer.

iShares MSCI Emerging Markets ETF

Tom Lydon’s clients own shares of EEM and EMB.