An ultimatum is "Do this, or else these things will happen." A compromise is, "Let's discuss our differences, and see if we can arrive at a mutually acceptable solution that gets us both at least part of what we want."

1) "There is a strong difference between an ultimatum and compromise. An ultimatum is defined as a final statement of terms or conditions made by one party to another, especially one that expresses a threat of reprisal or war. A compromise is defined as settlement of differences by arbitration or by consent reached by mutual concessions." Source and further information: http://www.blackplanet.com/your_page/blog/view_posting.html?pid=65504&profile_id=51519989&profile_name=SHER-real78&user_id=51519989&username=SHER-real78 2) "An ultimatum (Latin: the last one) is a demand whose fulfillment is requested in a specified period of time and which is backed up by a threat to be followed through in case of noncompliance. An ultimatum is generally the final demand in a series of requests. As such, the time allotted is usually short, and the request is understood not to be open to further negotiation. The threat which backs up the ultimatum can vary depending on the demand in question and on the other circumstances. The following are commonly encountered: in diplomacy, the threat to declare war, to take other military action or to impose sanctions such as trade restrictions or embargoes. in a kidnapping, the threat by the kidnappers that they will kill the hostages if their demands are not met In everyday life, ultimatums are also sometimes made in various contexts, such as in: a legal proceeding (e.g. the demand to strike a plea bargain or face a trial) a business relationship (e.g. the demand to accept a certain price or to forgo the deal) a labor dispute (e.g. the demand to grant a hike in salaries or another improvement in the employees' conditions, or face a strike) a personal relationship (e.g. the demand to desist in an extramarital affair or to face a divorce). Such ultimatums may or may not be legal and/or socially acceptable. Ultimatums are also a regular part of the crime of extortion." Source and further information: http://en.wikipedia.org/wiki/Ultimatum 3) "In arguments, compromise is a concept of finding agreement through communication, through a mutual acceptance of terms—often involving variations from an original goal or desire. Extremism is often considered as antonym to compromise, which, depending on context, may be associated with concepts of balance, tolerance. In the negative connotation, compromise may be referred to as capitulation, referring to a "surrender" of objectives, principles, or materiale, in the process of negotiating an agreement. In human relationships "compromise" is often said to be an agreement that no party is happy with. According cultural background and influences, the meaning and perception of the word "compromise" may be different: In the UK, Ireland and Commonwealth countries the word "compromise" has a positive meaning (as a consent, an agreement where both parties win something); in the USA it may rather have negative connotations (as both parties lose something). In the former Soviet Union, the word was rather unknown. (See Intercultural competence.)" Source and further information: http://en.wikipedia.org/wiki/Compromise 4) A compromise is a solution for disagreements which tries to satisfy both opponents approximately rather that satisfying just one of them perfectly. If one person is not satisfied with a situation, they could make an ultimatum to get their demand satisfied before a specific time. If not, they would harm the other side in some way. For instance, you could have agreed on a compromise, but one side has not implemented their part of the compromise. The other side would make an ultimatum to the other, asking them to implement their part. You could also get an ultimatum and try to discuss either about the demands or about the time where the demands should be implemented. You could make a compromise on better conditions for the ultimatum. Here an example: "The United States presented to key EU states a softened version of an ultimatum over Iran's alleged nuclear weapons program but diplomats said the text was still too strong to win approval at the UN atomic agency's meeting in Vienna. Washington dropped demands for the International Atomic Energy Agency (IAEA) to have unrestricted access to Iranian sites but upheld a demand that Iran suspend all activities related to uranium enrichment by October 31, according to a copy of the confidential text made available to AFP. "We're hoping we've found ground for compromise," a US diplomat said of the amendments submitted along with Canada and Australia to a draft resolution presented by Britain, France and Germany. " Source and further information: http://findarticles.com/p/articles/mi_kmafp/is_200409/ai_n6860059

The biggest difference is that an ultimatum is one-sided but a compromise is worked out with two people.