The symmetries provided by representations of the centrally extended Lie superalgebra psl(2|2) are known to play an important role in the spin chain models originated in the planar anti-de Sitter/conformal field theory correspondence and onedimensional Hubbard model. We give a complete description of finite-dimensional irreducible representations of this superalgebra thus extending the work of Beisert which deals with a generic family of representations. Our description includes a new class of modules with degenerate eigenvalues of the central elements. Moreover, we construct explicit bases in all irreducible representations by applying the techniques of Mickelsson-Zhelobenko algebras.As discovered by Beisert [1, 2, 3], certain spin chain models originated in the planar anti-de Sitter/conformal field theory (AdS/CFT) correspondence admit hidden symmetries provided by the action of the Yangian Y(g) associated with the centrally extended Lie super-This is a semi-direct product of the simple Lie superalgebra psl(2|2) of type A(1, 1) and the abelian Lie algebra C 3 spanned by elements C, K and P which are central in g. Due to the results of [6], psl(2|2) is distinguished among the basic classical Lie superalgebras by the existence of a three-dimensional central extension. It was pointed out in [4] that this phenomenon originates in some special Serre relations. A new R-matrix associated with the extended Lie superalgebra g is found by Yamane [15]. Furthermore, g can be obtained from the Lie superalgebras of type D(2, 1; α) by a particular limit with respect to the parameter α.The Yangian symmetries of the one-dimensional Hubbard model associated with Y(g) were considered in [2]; they extend those provided by the direct sum of two copies of the Yangian for sl(2) previously found in [14]. An extensive review of the Yangian symmetries in the spin chain models can be found in [13].These applications motivate the study of representations of both the Lie superalgebra g and its Yangian. In this paper we aim to prove a classification theorem for finitedimensional irreducible representation of g. Generic representations of g were already described by Beisert [3]. As we demonstrate below, beside these generic modules, the complete classification includes some degenerate representations which were not considered in [3]. In more detail, if L is a finite-dimensional irreducible representation of the Lie superalgebra g, then each of the central elements C, K and P acts in L as multiplication by a scalar. We will let the lower case letters denote the corresponding scalars,