The International Socialist Organization, or ISO, is a leftist organization which is currently (2007) inactive on the UCD campus due to lack of student interest as shown by scarce meeting attendance.
They hold lots of events that "organize activists... in order to mobilize opposition to all forms of oppression and exploitation." Some say these topics suggest George W. Bush is evil. There are a lot of flyers to these events posted on campus, each bearing a tagline "Handbill only. Do not post."
John Green was an officer of the ISO.
The ISO self identifies as a Marxist-Leninist-Trotskyist organization, which can be seen on their website which states that "The International Socialist Organization (ISO) stands in the revolutionary tradition of Karl Marx, Vladimir Lenin and Leon Trotsky." the books they sell, reading groups they have, the content of the news paper, http://socialistworker.org/ , which includes a "The Meaning of Marxism" column. Though, it should be noted that Marx's theories sparked philosophies that headed in many different directions and Socialism is, and has historically been, different than what some would see as "communism," it can be argued that the ISO in fact is a communist organization as seen by these people because it believes that "Capitalism must be overthrown," and as Leninists, they push for socialism as the intermediary step to communism.
To clarify the standard meanings of 'socialism' and 'communism', there are plenty of places you can read about it, though it appears that the ISO use the term 'socialist' though some would label them as a communist organization.
Where They Stand
According to Todd Chretien, Northern California Organizer for the International Socialist Organization, "...while we should fight for whatever reforms we can win — be it defending abortion rights, or strengthening the unions, or winning voting rights for undocumented immigrants, or working alongside the Greens to get independent candidates elected — whatever the reforms are, we believe that the point of a socialist organization is to say in the long term we need to build a revolutionary movement..." to overthrow capitalism.
More about them can be read here