The limited dexterity that existing hand prostheses provide to users contrasts with the manipulation abilities exhibited by state-of-the-art robot hands. This thesis explores the potential use of underactuated hands in the development of hand replacements with in-hand manipulation capabilities. Initially, the thesis presents a mathematical framework developed to analyze the ability of a given underactuated hand to manipulate objects in-hand. The framework comprises two parts:​ i) a methodology to model underactuated hands during the execution of in-hand manipulation maneuvers, and ii) mathematical tools to quantify the in-hand manipulation ability of a given underactuated hand. Subsequently, the thesis presents a case study using a specific underactuated hand architecture, representative of many existing underactuated hand prototypes. The hand presented in the case study is modelled and its ability to manipulate objects of different geometries is analyzed. Based on the findings, a manipulation strategy suitable for prosthetic applications is proposed. The strategy enables the hand to manipulate objects in-hand without any information of their geometry or physical properties. Finally, the thesis describes the experimental test conducted to validate the theoretical results.