Exchange-traded funds (ETFs) have become a powerful force in the world of investing. These baskets of stocks, bonds and other assets have surged in popularity and now contain nearly $2 trillion worth of both retail and institutional investor assets. Overall, ETFs are great building blocks for portfolios. But happens when the music stops? Some analysts and regulators have questioned ETFs’ ability to thrive in a world of low volume and zero liquidity. Here’s Aleph Blog’s David Merkel with more on the liquidity side of the ETF trade.

Financial Times (Tracy Alloway and Arash Massoudi): With ETFs, it’s all about that bid/ask spread and volume, volume, volume.

The Wall Street Journal’s Money Beat (Pat Minczeski and Alen Mattich): More on that lack of volume: You can almost hear the crickets above the ticker tape machine.

ETF.com (Dave Nadig): Despite these concerns, ETFs have been an amazingly good deal for retail investors.

Asbury Park Press (John Waggoner): The high-yield space has been especially kind to investors. But it’s time to sell your junk bond ETFs.

The Wall Street Journal (Jonathan Clements): Here’s how to build that ETF portfolio right. Index your way to gains.

Investing Caffeine (Wade W. Slome): How to adjust after the first half of the year’s various “surprises.” Some were doozies.

The Big Picture Blog/WaPo (Barry Ritholtz): Here’s exactly where you shouldn’t put your money. Stick to the indices.

Economic Times (Reuters Staff): It’s getting heavy here on “Merger Monday.” A massive global cement deal is getting more concrete.

Quartz (Michael Silverberg): Heroin bags as an objet d’art. It’s just like a Van Gogh painting.