Abstract. The paper is a survey of the recent theory of plurisubharmonic functions of quaternionic variables, together with its applications to the theory of valuations on convex sets and HKT-geometry (Hyper-Kähler with Torsion). The exposition follows some earlier papers by the author and a joint paper by Verbitsky and the author. §0. IntroductionOur goal in this article is to present a survey of the recent theory of plurisubharmonic functions of quaternionic variables, together with its applications to the theory of valuations on convex sets and HKT-geometry (Hyper-Kähler with Torsion). The exposition follows the papers [4,5,7] by the author and [8] by Verbitsky and the author.We denote by H the (noncommutative) field of quaternions. The notion of a quaternionic plurisubharmonic function on the flat space H n was introduced by the author in [4] and independently by Henkin in [24]. This notion is a quaternionic analog of a convex function on R n and a complex plurisubharmonic function on C n ; see Definition 3.1 below. On the one hand, this class of functions enjoys many analytic properties similar to those of convex and complex plurisubharmonic functions. On the other hand, these properties reflect rather different geometric structures behind them. This will be illustrated below by applications to convexity and HKT-geometry.We start with some analytic properties of quaternionic plurisubharmonic functions. In [4], the author proved a quaternionic analog of the Aleksandrov [2] and Chern-LevineNirenberg [19] theorems (see Theorems 3.4 and 3.6 in §3 below). It is worthwhile to recall these classical results now. The Aleksandrov theorem says that if a sequence {f N