Most people don't give much (if any) thought to eminent domain until it impacts them. Then it's essential to understand what rights the government has to take land owned by private citizens for public benefit.
Those rights are granted to local, state and federal governments. They're addressed in the Fifth Amendment of the Constitution under the "Takings Clause" as well as in the Fourteenth Amendment. However, the Constitution puts limits on that power. It also requires that the government fairly compensate people for the land it takes.
Note that "taking" property isn't the same as seizing it, as the government can do when property has been abandoned -- or in some circumstances when a person has committed a crime. The taking can be partial, complete or temporary.
It's also important to know how "public use" is defined. The government can only take property under eminent domain law if it will be used to benefit the public in some way. This used to be limited to things like transportation projects, parks and water supply structures. However, in 2005, thanks to a U.S. Supreme Court ruling, the legal meaning of "public use" was broadened considerably to include anything of community benefit. This could include hotels, shopping centers, gyms and even condominiums.
If the government decides to take land and/or property that is owned by private citizens, it will make them an offer based on the land's fair market value. The owner can accept the offer, contest the value or refuse to sell entirely. If an owner does either of the last two things, they'll end up in court.
If you're facing an eminent domain action, whether by a locality here in Colorado, by the state or by the federal government, it's essential to learn about your options and rights. Seek legal guidance from an experienced Colorado real estate attorney before attempting to deal with the government at any level over eminent domain.