The job of government CIO hasn't hasn't gotten easier, but it's certainly grown more interesting. CIOs at federal agencies are under pressure to adopt new technologies, deliver on the promise of "open government," and shed outdated procurement practices. At the state and local level, the pressures are much the same; the resources, often less.

How are CIOs managing these challenges? InformationWeek and our recently launched InformationWeek Government set out to identify top technology leaders at all levels of government who are embracing and responding to these new expectations. Our top 50 is a Who's Who of government IT influencers from San Francisco to Washington.

One of the things that sets government IT apart from most corporate IT departments is sheer scale. It's one of the first things that federal CIO Vivek Kundra points to when he talks about the task at hand. Federal agencies spend a combined $76 billion annually and manage more than 10,000 systems, in support of 1.9 million employees and 300 million "customers."

Kundra is challenging his peers to manage all of that more effectively, efficiently, and securely, while exposing data feeds in the interest of government transparency. He wants federal CIOs to concentrate less on infrastructure and more on "unlocking value." To do so requires fresh approaches--cloud computing, social media, development competitions, bite-size IT projects.

CIOs in many government offices are responding. Our list includes IT leaders from the Department of Defense, NASA, the intelligence community, and civilian agencies, in addition to cities and states. There are a handful of non-CIO titles here, too--executives such as Jeffrey Zients, the Office of Management and Budget's chief performance officer, whose responsibilities are joined at the hip with those of federal CIO Kundra and federal CTO Aneesh Chopra.

Some of these CIOs you'll recognize; others keep a low profile. All have their work cut out for them. Read our profiles of the entire Government CIO 50.