This thesis studies the design of an architectural platform for realizing a set of selected applications into a single system sharing hardware resources while being power efficient. We refer the resultant systems as a Multi-Mode (MM) system since it can be configured to operate in multiple modes or configurations. We start our study with the switching activity model and estimation technique for components under resource sharing. The first phase of study aims to gain a basic understanding of the impact of resource sharing on power consumption. We then present scheduling and allocation algorithms based on the switching activity of a resource with and without sharing. We show that the algorithms effectively reduce datapath switching power under resource and timing constraints. Finally, we present a design methodology that addresses the synthesis issues of MM systems, and study how the MM systems can better meet the power dissipation, performance and flexibility requirements. Results demonstrate that MM systems can achieve more than an order of magnitude improvement in power over FPGAs with a fraction of power overhead over single-mode designs. Easy and fast reconfiguration coupled with efficiency in terms of area and power consumption makes the MM system a viable solution for future mobile applications