Even low-cost ETFs need to generate revenue to cover their costs. Plenty of ETFs fail to garner the assets necessary to cover these costs and, consequently, ETF closures happen regularly. In fact, a significant percentage of ETFs are currently at risk of closure. There's no need to panic though. Broadly speaking, ETF investors don't lose their investment when an ETF closes. A closure can, however, be inconvenient and costly. Read our guide on managing and avoiding ETF closures just in case you find a closing ETF in your portfolio.