This paper presents a 3D CAD system to design sockets of lower limb prostheses, both transfemoral and transtibial. The proposed system, named Virtual Socket Laboratory, can be seen as a virtual laboratory where the user has at her/his disposal virtual tools that permit to emulate the procedures applied by orthopaedic technicians during the traditional socket manufacturing. The module is centred on the digital model of the patient and is based on the specific domain knowledge to guide the user during socket modelling suggesting the most appropriate design rules and procedures. First, main steps of the new design-modelling process and system functionalities are presented. Then, for each step, procedures carried during the traditional proces...