The case is a big deal because the law affects everyone from academics to cyber-security researchers to consumers. Companies, including Intel and Sony, also have a stake because they often invoke the law to protect their intellectual property.

To get a better idea of what the case is all about and why it matters, here’s a plain English Q&A describing the main issues.

What is this copyright law that’s so controversial?

The dispute is about one part of the Digital Millennium Copyright Act (the “DMCA“), a 1998 law intended to protect intellectual property rights, while also encouraging innovation and free expression on the internet.

This week’s lawsuit doesn’t take aim at the whole DMCA, but instead at one part of it that makes it a federal crime to interfere with copyright protection software or to engage in some types of reverse engineering. The law also creates a process where the Copyright Office grants exemptions every three years for certain activities—such as turning a CD into a digital file, or tweaking a phone’s software to use it on a different cell network.

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Critics say the law is too broad and can ensnare activities that have nothing to do with copyright infringement, while companies claim they need it to stop piracy and hacking.

Who is bringing the lawsuit?

One plaintiff is Matthew Green, a computer science professor at Johns Hopkins University. He claims the DMCA interferes with his ability to conduct or publish cyber-security research since he is afraid of being sued.

The other is an engineer named Andrew “bunnie” Huang. He says the DMCA prevents him from building a selling a product that would let people enhance video streams by, for instance, adding live comments. Huang says he is afraid Intel (INTC) will sue him because his technology relies on getting around software restrictions that block people from viewing HDMI signals.

What are the free speech issues?

Green and Huang say the DMCA violates their First Amendment right to free speech. Specifically, they say the section of the law in question is too broad because, under the goal of protecting copyright, it sweeps up too many lawful activities.

The men also say the section is an illegal “prior restraint” that forces them to get permission before they can speak—in this case “speaking” means publishing security books or writing code. They add the Copyright Office’s exemption process is too slow and cumbersome to address these concerns.

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The U.S. Justice Department, whose job it is to argue in favor of laws passed by Congress, has yet to respond to the lawsuit. When it does, the agency will probably say the law protects copyright without harming speech (especially because of the exemptions), or that the case doesn’t really involve free speech in the first place.

What do they want?

The men are asking the court to issue an order saying the section of the law violates the Constitution, and to strike it down. They also want a declaration stating the Justice Department can’t prosecute them, and that what they’re doing counts as an exemption.

Will the case succeed?

Obviously, no one can no for sure what the court will do. But it’s worth noting Green and Huang are not cranks or copyright pirates, but are a well-respected professor and engineer, respectively. The case is also being run the Electronic Frontier Foundation, a civil liberties group that has considerable legal fire-power. The group likely sought out Green and Huang to be the face of the case because they are sympathetic plaintiffs.

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Finally, it’s likely corporations and trade groups will ask to intervene in the case, with big tech companies siding with Green and Huang, and the entertainment industry asking to preserve the law. (The music and TV industry, in particular, have argued the DMCA rules against fiddling with software are necessary to prevent people from distributing their content without permission.)

Those opinions could shape the outcome.

Anything else to note?

Yes, this case is likely to create further calls for Congress to reform the DMCA, and this could open a whole can of worms. While the anti-circumvention rules at stake here have long been contentious, they are just one part of a larger debate over the DMCA.

If Congress decides to re-examine the DMCA, you can be sure the entertainment industry will use the occasion to try and erode the law’s “safe harbor” rules, which protect websites from getting sued for copyright infringement so long as they abide by certain measures.

Finally, if you want to read more about this case, the EFF has helpful posts on the constitutional arguments and on how the law affects remix culture. Ars Techica has a good summary too, and Huang explains why he is suing on his “bunnie” blog.