Welcome to our special Post 200 edition of Capital Business.

Ordinarily, our pages would be filled with the latest news on government contracting, commercial real estate, technology, banking and the business of law. But this week we take time out to focus on the region’s very biggest — the companies, law firms, nonprofits and other organizations that power our local economy.

It doesn’t take too long to go through the list to realize just how diverse the greater Washington business establishment has become, and how connected we still are to the fortunes of the federal government.

Government contracting is big business here. Four of the five largest public companies are defense or federal contractors.

It’s also remarkable to see how stable our business community has been, despite the recent global economic turmoil. This year’s list saw the departure of just nine organizations from last year’s accounting, and nearly all were replaced by larger firms.

For instance, defense giant ATK moved from Minnesota to Arlington, and claimed No. 15 in our ranking of public companies. Vangent, an Arlington contractor that was once one of our larger private companies, was gobbled up by Falls Church-based General Dynamics.

Volkswagen of America was knocked from the list of foreign-owned companies when Canadian contracting giant CGI bought Arlington IT purveyor Stanley, adding to its U.S. workforce already here. Comcast edged out Target in terms of full-time employees working in the region.

Some companies changed lists. Public companies such as contractor SRA International and Blackboard, the online education firm, were taken private. Private RLJ Cos. created the public RLJ Lodging Trust of Bethesda, and so became our choice for the list.

A few Post 200 stalwarts face uncertain futures. Mortage finance giants Fannie Mae and Freddie Mac remain under government control as Congress weighs what to do with them. Other firms have been buffeted by the economy and their place is tenuous at best.

There are plenty of companies knocking on the door to take their spots. We considered whether to add a category to capture fast-growing upstarts such as daily deal purveyor LivingSocial and energy data firm Opower. But in the end, we opted to focus on the big because most have stood the test of time, in good economies and bad.

And as our cover story on the employment picture shows, big companies still wield a lot of influence locally in the creation of jobs.

— Dan Beyers