Argumentation aims at increasing acceptability of claims by supporting them with arguments. Roughly speaking, an argument is a set of premises intended to establish a definite claim. Its strength depends on the plausibility of the premises, the nature of the link between the premises and claim, and the prior acceptability of the claim. It may generally be weakened by other arguments that undermine one or more of its three components. Evaluation of arguments is a crucial task, and a sizable amount of methods, called semantics, has been proposed in the literature. This paper discusses two classifications of the existing semantics: the first one is based on the type of semantics' outcomes (sets of arguments, weighting, and preorder), the second is based on the goals pursued by the semantics (acceptability, strength, coalitions).