The fund invests in global clean energy companies, which is defined as those involved in the biofuels, ethanol, geothermal, hydroelectric, solar, and wind industries. Aside from holding companies that produce energy through these means, XCLN also includes companies that develop technology and equipment used in the process. Selected by the index committee, the fund is weighted by market-cap and exposure score, subject to several constraints. The index is reconstituted on a semi-annual basis.