Philosophers weren`t thinking a lot about terrorism before the terrorist attacks in the United States on 11 September 2001, or even when they were thinking the main concern was how to deal with terrorism. But after this terrorist attack terrorism was high on the philosophical agenda mainly manifested as an ethical problem. The key concern was: can terrorism be morally justified? That is the issue we are dealing in this paper too. But, the answer of this question largely depends on the treatment of terrorism, i.e. from the answer on a previous question: what is terrorism? With regard to the problem of defining terrorism the dominant approach seeks to acknowledge the core meaning “terrorism” has in common use. That is why we are going to give some various definitions of terrorism from which the ethical problem of terrorism arises. Aftermaths we will make an overview of the most important theories and philosophers that are dealing with this question. We will consider the two main approaches to this issue. Namely, in ethics there are two main approaches: consequentialist and nonconsequentialists. First ones are judging ethical issues based on the consequences second ones the moral status of the ideas nevertheless of their consequences. In the case of terrorism that would mean that consequentialists propose to judge terrorism, like everything else, in light of its consequences. Nonconsequentialists argue that its moral status is not simply a matter of what consequences, on balance, terrorism has, but is rather determined, whether solely or largely, by what it is. For the consequentialists, the test of terrorism is what is done, for the nonconsequentialists what the ultimate aim of doing it is. And this distinction is not merely just formal. In this paper we will clarify those distinctions