Exchange-traded funds, or ETFs, have existed since 1993, according to Forbes, though they became much more common in the early 2000s. Since then they have risen in popularity, with net assets held by ETFs currently amounting to $1.34 trillion. There are several options when it comes to investing in silver ETFs. For instance, some ETFs invest solely in physical silver, or only in silver futures from a particular exchange. Others invest in the silver mining industry itself. Investors should learn about each type in order to determine which best suits their needs. Below is a look at five silver ETFs worth considering. iShares Silver Trust (ARCA:SLV) As the iShares Silver Trust's website warns, it is not your standard ETF. More specifically, iShares is not an investment company registered under the Investment Company Act of 1940 or a commodity pool under the Commodity Exchange Act. Further, its shares aren't subject to the regulatory requirements that apply to mutual funds. Investors who are not put off by those conditions may find the iShares Silver Trust appealing. It uses the London silver fix price as its benchmark and holds silver bullion — 10,045.79 tonnes, to be exact. Its net asset value clocks in at $6,417,002,948, and since its inception, iShares has achieved returns of 5.77 percent for its investors. Sprott Physical Silver Trust (ARCA:PSLV) The Sprott Physical Silver Trust is also an alternative to the traditional silver ETF, although in its case it is an option for investors interested in holding physical silver. It has a total net asset value of $960,691,854. The Trust stores its silver at a secure third-party location in Canada where it is subject to periodic inspections, its fact sheet states. Investors who own a certain value equivalent in dollars can redeem their units for physical silver each month, and it can be delivered nearly anywhere in the world via armored carrier. The Trust only invests in London Good Delivery physical silver bullion, less the 3 percent of net assets devoted to expenses and anticipated redemptions.