OAKLAND, Calif. — FTSE Group has launched an environmental technology index made up of 50 of the largest green tech companies around the world.

FTSE worked with Impax Asset Management to choose the company that make up the FTSE ET50 Index from 500 stocks. The index tracks companies that specialize in environmental technologies, such as alternative energy and efficiency, waste treatment and pollution control.

The companies have an investable market cap of more than $161 million.

The release of green-focused investment vehicles is part of a growing trend. Earlier this month, for example, Standard and Poor's unveiled its Global Eco Index to measure the performance of 30 of the largest public companies that profit from eco-related technologies.

The Global Eco Index covers companies in 12 countries with an adjusted market capitalization of $388 billion.

In March, S&P launched its Global Thematic Index Series which is composed of three indices: its Global Clean Energy Index, Global Water Index and Global Infrastructure Index.

Merrill Lynch launched its Energy Efficiency Index in August to track 40 global companies in four sectors that will probably profit from energy efficiency.

And just last month, Barclays Capital launched the first global index to follow the performance of carbon credits and the carbon emissions market.