Modelling and analysis of an electromagnetic generator designed for harvesting power produced during walking is presented. The generator is designed to be unobtrusive to the user by embedding it within the thickness of a normal shoe sole, and by applying a passive generation principle which requires minimal additional force over that normally exerted by the user during walking. In this way, a portion of the power used in walking is harvested for potential use in powering portable electronic devices. Analysis of different geometrical and material properties is applied to identify conditions for optimized designs; average power levels of up to 14 mW (200 mW of instantaneous power) are demonstrated within a volume of 15 x 15 x 100 mm(3) at a walking speed of 2 steps per second. At least two of these volumes can be easily accommodated within a shoe heel to provide up to a 56 mW average power per user, and higher power levels can be achieved for faster walking or running speeds.