U.S. immigration laws contain numerous grounds upon which non-citizens may either be deported back to their country of origin (the technical term for which is "removed") or refused entry into the United States. In fact, the laws divide these grounds into two separate categories:
There are waivers and exceptions to some of these, but you'll want to speak with an attorney for the details.
If U.S. immigration authorities believe that you are deportable, or that you were inadmissible during your last U.S. entry, removal proceedings may be started against you. You will have a chance to argue your case and in some cases to ask for a waiver (legal forgiveness). However, this might occur in the context of deportation and removal proceedings in immigration court. In any case, you'll want a lawyer's help with this type of issue.
Once an immigrant becomes a U.S. citizen, they cannot be removed unless they used fraud to gain citizenship or another immigration benefit. As soon as you are eligible, obtaining U.S. citizenship is a good way to safeguard your status in the United States.
Learn more about defending yourself from Deportation.
Here's a brief summary of the types of personal characteristics or history that can make someone inadmissible to the United States.
Again, this is just a brief summary, intended to highlight potential trouble areas. Do not attempt to analyze your personal immigration situation based on this list.
For more on being "inadmissible," see Who Can't Get Into The United States?
Here's a brief summary of the types of personal characteristics or history that can make someone deportable from the United States.
To read more about the grounds of deportability, see Can I Lose My Green Card and Be Deported?
In short, while there are clear distinctions between the grounds of inadmissibility and the grounds of deportability, both can present serious problems for non-citizens in the United States or seeking to enter. Consult an experienced immigration attorney with any questions or for a personal analysis.