An interdisciplinary environmental master’s degree is usually a professional degree; it prepares students for specific careers in environmental policy and management.  These degrees may go by many different names (Master’s in Environmental Policy, Master’s in Environmental Science, Master’s in Sustainability, etc).  The kinds of jobs they prepare one for are quite varied.  Many become consultants or analysts in private corporations or government.  These degrees may prepare one for a variety of land and wildlife management positions (like managing the Arboretum).  Some go into law enforcement—for example, working for US Fish and Wildlife to enforce the Endangered Species Act.  Many will work for non-profits, performing a range of management, education, and policy tasks.

Some programs will give you information about what their graduates are doing on their website.  For example, University of Michigan has this helpful link:

http://www.snre.umich.edu/career_services/job_placement_statistics

The advice for getting into one of these programs and for choosing a school is similar to the advice for getting into and choosing an interdisciplinary PhD program:  You’ll need a good GPA (at least 3.0, and 3.5 for the more competitive programs).  You may need to take the GREs.  Usually no particular coursework is required, but some calculus, natural science, statistics and economics is usually desirable. 

There are many, many of these master’s programs popping up all over the country, and no rankings to help you evaluate their quality.  Research them carefully, with close attention to how well-established they are.  (This will affect the size of their alumni network, which is one of the principal benefits of getting a graduate degree).  A good program won’t be afraid to post information about their job placement rates.  Bear in mind that many graduates of these programs may have dual degrees; an interdisciplinary environmental master’s alone may not be sufficient to be competitive for the best jobs.

Consider cost as well; a master’s degree can be valuable, but it won’t increase your earning capacity as much as, for example, a JD.  So you’ll want to avoid going too deeply into debt.  Many graduate programs offer fellowships or teaching or research assistantships, and these can dramatically decrease the cost of the program—but remember, you’ll also be losing a couple years of earnings while you’re in school.  You should consider that cost as well.